What stakes should I play with a $4000 bankroll?

I'm currently playing $30 - $50 sit n goes or multitable tournies with $50-$150 buyins. Lately, I've been experiencing some huge swings in my bankroll. I'll lose $1000 in a few hours, then win $1200 during the next few hours. It seems the players at the higher stakes are a lot more aggressive and willing to gamble compared to the players at the stakes I used to play ($10 - $20 sit n goes), where the play is fairly conservative even late game.

Anyway, what is the correct stakes I should be playing?

lol, I'm in the wrong place. If I had $4000 in online poker, I'd be buying a new computer, not wondering where to go to make more.

here's what I would do if I were you. Play in a $4,000 HU match against someone with the sn zachvac. Fold top 90% hands and shove with bottom 10% of hands. That should double you up in no time and give you plenty of BR to experiment with

$50 tournaments is right for your bankroll. But, IMHO, it depends on what you want out of your game. I play way below what I could because I just want to play and a little over break-even lets me do that all I want.

It depends on how comfortable you are with your own play I guess.

I have a current bankroll of ~$2,500 and play $100 SNGs. Roughly following Chris Ferguson I make sure that after I've bought into an SNG my bankroll still contains 20x the buy-in.

This means that if I had a BR of $2,060 I couldn't play a $100 SNG because after the buy-in I'd have less than $2,000 left (note that I always ignore the fees because it's easier to calculate).

As for MTTs, the rule is identical, but I want to have 50x the buy-in left, so with your bankroll I would not be playing $100 MTTs.

The reasoning is quite simple: it's harder to cash in a MTT than it is to cash in an SNG. For MTTs, usually 10% of the players make it into the money while it's 30% for SNGs.