Highest cash game I've played is 3/6 limit. Haven't really tested the higher NL levels, .50/1 is the highest if I remember right. Highest sng I've done is $100, I didn't cash, lol. I've done four $50 sng's, cashed in all except one. Highest MTT buy in I've tried is $30/3, although the most I've spent on one MTT was $60ish in an $11 rebuy. Pretty impressive stuff, I know.
Edit: I did play in a $215 MTT on Party a long time ago, but I won my seat for $11 or something so that's all I had invested.