I've actually had a very long discussion recently with a friend of mine about this, a high-stakes HUNL reg. His thoughts: You need 40 BIs for HU, 30 BIs for 6max, and 20 BIs for FR, regardless of whether you play full-time or recreationally, because if you lose more than that then that's more than just variance. It means there is something seriously wrong with your game, and you need to take a break and reevaluate.
Of course if you play full time you need more money than that because you need a liferoll to handle drought periods, but that money goes completely separate from your poker roll. Like for instance, if you're playing 2/5 live for a living and your monthly income allowance (gotta set some $$$ aside to put back into BR) is $2,000, then you should have at least $12,000 set aside as a liferoll, and THEN 20 BIs at 2/5 (that would be $10,000). So your combined roll would be something like $25k.