[Harv72b]

First of all, any time you're looking to move up in limits, take a shot first. Meaning, set aside some surplus from your current bankroll & take that to the higher limit...for example, you're currently playing .50/1, and let's say you've built up $600. Take $100 of that & give 1/2 a shot; that's 50 BBs which gives you two standard buy-ins, or plenty enough to take a stab at the higher limit. If you do well & build up your stack, then you're probably ready skill wise as well as bankroll wise to make the permanent move up. If you drop the $100, no big deal...you go back to .50/1, work on your game, and try it again a little further down the road.

The reasons I suggest this is that, first of all, your competition will improve as you move up in the limits. From what I remember the jump from .50/1 wasn't too severe in that regard, but that may have changed. At any rate, even if you're mopping up in the .50/1 games, it could be that you're currently just a break-even or even losing player vs. the competition you'll see at 1/2. Second of all, there's always something of a chip shock when you move up to a new limit, and you suddenly look down at your stack after losing 1 big pot & realize that you've lost in that one hand what would've taken you hours or even days to win at your old limit. That can cause you to play tentatively, which is never good poker; by just setting aside a small portion of your surplus bankroll, you can comfortably play good, aggressive poker at the new limit without worrying about crippling your 'roll.

As far as your core question, at least up through the middle limits the 300/500 BB rule really doesn't change. More is always better, though, and of course the standard clause is that you have to be a good enough player to win at the new limit in order for any bankroll to be large enough.