The information I will be providing is from this website http://www.geforce.com/Optimize/Guides/how-to-get-rid-of-lag-guide
Also, it talks about PC games, however, some/same priciples still apply to the PS3.
The site talks about "Graphics Lag", "Stutter Lag", "Control Lag", and "Ping Lag".
"Graphics Lag" is associated with Frames Per Second. According to the article if a game goes below 30 Frames Per Second, then your eye will start to notice the impact. Remember the human eye can't notice anything above 30 Frames Per Second. So MW3 was said to run at or above 60FPS. That is not the case, both the 360 and PS3 version drop at times in the campain below 60FPS, and sometimes go into the 40s. Footage can be seen here: http://www.youtube.com/user/AkajiCZ#p/u/15/a6tA-AqC0rA
For Call of Duty: 4 Modern Warfare Frame-Rate compariosn look here: Call of Duty: Modern Warfare Xbox 360/PS3 Frame-Rate Comparison
For Call of Duty: Black Ops Frame-Rate comparison look here: http://www.youtube.com/watch?v=bV-lBso4-VA
Now in all the videos I have not seen the Frame-Rate in the game go less than 30, so when people complain about the frame-rate, they are actually being mislead. The reason it goes down so much in single-player campaign is because there is so much more going on at once than in MP. There are more than 12-18 AI at a time attacking you, explosions, and vehicles moving that the FPS can drop down. But it's never noticable when we play. So what in MW3 MP are we seeing?
Well "Control Lag" is basically non-existant on PS3 and is more to do with PC players and their drivers they run. On PS3, however there are two options to how your controller is sending data to the PS3. One is by Bluetooth, and the other is by USB. On PS3, having your controller connected to a USB cable will provide a faster response time in your controls. But the difference between USB and Bluetooth is so small on PS3 that it should not be a concern, but the technicality is there.
In MW3, I beleive with the best of this knowlege we are seeing a combination of "Stutter Lag" and "Ping Lag".
Here is the source's definition of "Stutter Lag":
"OK, so you think you're getting enough frames to remove graphics lag from your list of culprits. How come things still aren't smooth? Enter Stutter Lag, which occurs during periods where the game appears to stutter or momentarily freeze. To understand this problem, you need to picture the chain of events which lead to the game image appearing on your screen, as detailed here. Basically, all game data has to first load up from your drive before your CPU and graphics card (GPU) can do anything with it. At various points that data is held in temporary storage areas such as your system memory (RAM) or video memory (VRAM) to help your CPU or GPU access it more quickly when it's needed. You can see that there are several areas which could be to blame for game data not flowing smoothly through your system. When that data hits points where game information is not being transferred fast enough, you get stuttering and momentary freezes."
Sounds familiar right.
The 3 tips to optimize or reduce this is:
1 - Upgrade your HDD(Harddrive)
2 - Upgrade Ram
3 - Upgrade GPU
Well 2 & 3 on PS3 can't be upgraded, but your can upgrade your HDD. The article actually stataes that stuttering is most likely to occure due to your HDD. As most of us have 5,400RPM drives it could easily be our HDD, as those are crappy and the access time(Latency) is slow. Now COD4 and MW2, when playing MP never accessed the PS3's HDD, give it a shot yourself. Go to Black Ops, and the HDD is constantly being accessed, CONSTANTLY. And that game I have really bad stuttering, which I thought at the time was bad Frame-Rate, but it would seem as that was a misleading observation. MW3 is constantly saving the the HDD now with theater mode videos being saved to the HDD, rather then the sever like BlackOps. With our 5,400RPM drives, that access time(Latency) is over 5.00ms. Maybe worse depending on other factors. PC player know as well as I do that heavy gaming on a 5,400RPM drive on PC sucks even with tons more RAM and CPU/GPU power. So could it be that our slow PS3's stock HDD along with Call of Duty's high demand for constant data is bottlenecking are gameplay?
If so, the answer is a simple yet expensive fix. What we would need to do is upgrade out PS3's HDD to an SSD(Or Solid State Drive). With no moving parts the access time(Latency is of 0.08-0.16 micoseconds. Not to mention faster Transfer Rates as well. Along with no heat output. I will be buying a SSD drive, and will report back with my findings. Remember MP is always saving with Theater Mode videos going to the HDD, so when people have reported the game running better with it off, it would make sense that the stuttering is less, as load on the HDD is a lot less. Turning Theater Recording Off doesn't improve your internet latency because no information is being saved to the server like on Black Ops.. So this would presume the stutters are entirely from the slow 5,400RPM HDD. IW/SH probably use better hardware, or porting from 360 caused this instability.
As with "Ping Lag" I don't need to explain it.
Don't shut this theory down, it makes plenty of sense.
Note: Also, I hate to say it, but it has been proven that the PS3 Slims runs games better. It was optimized to run games better. Some test were done to compare the FAT and the SLIM. The Slim performed faster on games booting up by just a few seconds . But I beleive that had to do with the motherboeards getting smaller and through normal sliming of the componets, the system actually was a bit faster in processing data. I remember a guy on the Black Ops forums saying he had a FAT and a SLIM, he said switching the he SLIM solved decreased the stuttering on Black Ops. But take that with a grain of salt for now. I wonder if the FATS are more affected, IW/SH would be testing on SLIM PS3 and Black Ops would have been tested on SLIMS as well. Maybe the processing diference affected the output on the FATS. Would be really stupid.
This was stated by a user named "Paperrell" on the Black Ops forums regarding the stuttering:
"I Installed a WD 250GB SATA @ 7200 RPM in my "FAT" PS3..... I did it for the space needed but the Maps all load about 1.5 X faster than the 80GB that was in it... Later due to "lock ups" and "stuttering" (as you put it) I upgraded to the PS3 SLIM 160GB and installed my 250GB in it..... ALL MY PROBLEMS ARE NOW GONE!!!! Maybe you should backup you files (everything) go out trade in your old PS3 and get a new one (which I did).... not counting the new HDD I saved $150 on the new purchase at EB GAMES/GAME STOP (with a couple old games with the trade in). For me it was the "FAT" PS3 that was the problem."
Now you see why I brought it up.
And even if Activision or IW/SH games new it was the slow HDD, they wouldn't say anything because they would either have to blame Sony for the hardware which would backfire because other games run perfect on PS3, so then it would backfire to the devs for not properly optimizing the game to work with the PS3. They could reccomend ugrading the drive, but then people would backlash and say "Now I have to buy a new HDD and spend money just to play your game because you didn't optimize it right". You see the issue here, we have to solve this crap ourselves now to make the games run better.The SSD might just be the leap forward, unfortuantely an 80GB SSD drive at the cheapest will run $150 bucks on Amazon.
Update: Final Impression!
The SSD has solved all stuttering on MW3 & Black Ops. It's Solved all issues on Skyrim, which had massive stuttering. Read about it! This project was fun, but best of all it got the results I wanted. Read my last few comments.