As Norton posted above and I think I have posted somewhere here as well (I know I posted some stuff on UPF) check out the posts on standard deviation and win rate to get a pretty accurate picture of what kind of BR you need for a certain limit.

I have never lost more than 150 BB over my ten year career but I have hit that number once in a single session of 10-20 with a half kill in a live game in New York in a disasterous session. I have been down more than 100 BB multitablling in a days time on several occasions but most of the time recovered the losses the same day or most of it. If you have a low variance type of game like myself 200 BB should be more than enough to sustain you at the lower limits but if you fancy playing QJs in EP then you will need substantially more