To be honest, my own rule has always been 10 buy ins minimum to move up. However, that was always dependent on how I felt the level of play at the new stakes was relative to my own. I would say give it a shot for a bit. Find a number that you are comfortable losing before deciding to drop back to 10nl.
One thing to be aware of: if you decide to move up and test the waters, dont change your overall strategy right away. Dont get intimidated by the stakes and tighten up, or become less aggressive, whatever it may be. Play the game that has made you successful to this point. Obviously, adjust as necessary as you get acclimated to the new level, as there will likely be changes to your game to maximize profit. But my advice is to let your game evolve while playing, rather than change prior to the jump. A change is more likely to mean losses and not give you a true sense of where your game is relative to the other players.