You can set a nitty Bankroll requirement, but big win rates achieve even nitty standards for moving up rather quickly. Let it be bankroll driven. If you're unsure of your readiness level, set a nitty stop-loss move-down limit so you don't destroy 2/3's of your roll before moving down. That way, if the first shot doesn't work out, it's just a couple of weeks and then back up.

My multiple shots at 25nl are well-publicized on FTR. I'm there and winning now. Turns out I'm a bankroll nit, and get VERY weak-tight if I'm under-rolled. I got to $800 this time before taking my shot. Having 30+ BI made my whole game better, more confident and reasonably aggressive. Choose a BR limit that let's you play your game. When you're monies are there, move up and pwn it.