I went ahead and prestiged the second time hoping to get the extra class slot, but unfortunately, you don't get the next one until prestige 3. I'm starting to wonder if its even worth it because I love my Tar-21 with extended mags.
You level up to the Tar pretty easy once you prestige. I forget what level you get the Tar on but i remember getting it real quick. When you prestige, you can get to level 25 in one night easily. It's once you get to level 25 or so that it takes alot more xp's to prestige. I am loving the Tar with silencer. The iron sights are the best in the game so i don't have to use bling. I am pretty close to getting blue tiger for it.