Well, my MKIV must've been broken cause it wasn't nearly as cool as everyone who loves them makes them out to be. The Clean channel was among the best I've ever heard, problem is, I have little to no use for a clean channel. So that leaves the lead channel and to be honest I like the MKIII, .50Cal+, and Studio Pre's lead channel better.
My main amp is a highly modified 1990 .50Cal+ head. I took it to Kendrick amps here in Texas and told them it wasn't loud enough. I had them install 100 watt output and power transformers. And now it's powered by 2 6550's. Problem is, the other guitarist in my band uses a MKIII, which is a lemon, he's had it in the shop more than he's used it. He has no back-up, my back up is my Studio-Pre/2:90. He's using my .50Cal right now.
Why do I keep coming back to the Studio, it's simple, has a nice clean channel and a great lead channel, and it's simple like my .50Cal+ but with a few more options...