Those bankrolls are too small by a factor of 2.

20x buy-in for NL
20x buy-in for SnG
300x Big Bet for Limit

That being said, I know of good winning players who have had swings that would do serious damage to any one of those bankrolls.

My personal worst swings (so far)
NL: 12x buy-in
Limit: nearly 150BB

Also, having a thick bankroll will give you the confidence to make aggressive, winning plays.