These games are tough for building a bankroll from FRs. The odds are against you if you're trying to cash with one buy-in, and with 3.5 hour late reg its easy to think you would need an average 10 buy-ins to get to the end of late reg. So if these are your type of game, then you really would want to already have a BR of at least 100 buy-ins (personally i'd like 300) to handle the high amount of variance. You need to build a deep stack going to the bubble to win these donkfests. I personally hate rebuy touneys because the variance is too high for my taste.