15 or higher solo on the tier 3 and 4 maps is pretty good. Wave 17-19 will get you top 10,000 on the leaderboards on a bunch of those maps (xbox).
For the standard maps I think top 10,000 is worth bragging about.
For the DLC maps I think top 2000 is about the equivalent.
decomission level 35 solo, terminal 32 solo, offshore 25 solo and i cant seem to get past 25 solo, i find solo easier than playing with randoms online, so i mostly do that, if anyone wants to team up message me xbox live