Wade, I’m also 6′ and 200 lbs, running Rotax Masters. I run an Italkart Rapido V, all 30 mm frame. Most of the guys at my club in our class run OTK (Tony, FA, Kosmic), CRG, or Energy karts because that’s what’s supported here by local dealers. Within the OTK, CRG, and Energy crowd, there is a mix of 30 and 32. I wouldn’t say any brand or frame size is better than or has an advantage over another. It really comes down to driver and ability to tune.
There is no local Italkart dealer in my area, but I’ve been around the sport long enough that I can survive without the at-the-track support. Honestly, the only reason I run the Italkart is I’ve got a history with IM dating back to the early-90’s – they treated me real well and I haven’t forgotten that. If I had no history with IM, I’d probably be on a Tony or CRG too for the at-the-track support – like I say, they’re all good chassis.