I use a Peavey Valveking through a Framus Dragon 412 ST, clean boosted with an SD-1 and it is MEAN. I'm using a Dean caddy with an SD JB in the bridge. I don't know why you'd want any more gain, to be honest. My band plays anything from crystal cleans to Bloodbath-esqu trem picking, and it does both, and does it well. But, as someone said, it is VERY cab dependant. I was using it with a 1960a for ages, and it sounded pretty wank. Then for a while I was using a Sheffield loaded 412, and it sounded worlds better. The V30 Framus I'm now using is just perfect for this head. It seems to divide up bass and clarity, and give you perfect measures of each. I love it.
Speaking of cab dependant heads, the second guitarist in the band uses an Engl Invader 100 through the aforementioned Marshall 1960a, with an LTD F-400 with EMG 81's, and it sounds like shit. At first we thought it was the EMG's that just didn't work with the Engl, seen as my JB's sounded marginally better, but ploughing the Engl through the right cab is brutal. I can whole-heartedly guarantee that Seymour Duncan JB+Valveking+Framus Dragon 412 sounds MUCH better than EMG 81+Invader+1960a, hands down. But the Engl through the right cab (current favourite is the Blackstar Artisan 412) is possibly the nicest sound I've ever heard.