Bankroll Management is the biggest key. I would say there's not much differnce between 5NL and 10NL, since a lot of sites don't have lower than 10NL (FT and Bodog, just to name a couple). I do think the 10NL at Stars is tougher than full tilt, because more people have been grinding it up.

That being said, I've been known to take a shot above my BR from time to time, just to see what it's like. Trust me, there are horrible players at 50NL and higher, so it can be beat. You just have to have the proper bankroll to sustain at those levels.