Couple things...
Ubers: You dial them in by ear, NOT eye. The EQ/parameters are very coincidental and counterintuitive. Add one thing, it takes away from another, lessen a global, suddenly everything changes on the preamp EQ. They're tricky lil' mofos to setup when you're used to any number of other more "normal-to-dial-in-amps", but once you get the hang of it (and trust me, your knobs will look VERY different than, say, someone running a JCM800 or a Splawn or any other amp - even another Bogner for that matter) - when it's finally where you want it. Forget the eye, go by ear. I tend to start with my globals at 11 o'clock, and work the pre-EQ from there. Once it's close, then I start playing with the globals and really pay attention to what's being given or taken away. Trust me though, great, great amps - period.
20thA Sheevs? Only head that I like that runs KT88s. KT88s are one of the most transparent super-output bottles on the market today. They don't colour the tone - hence the reason manufacturers like Fryette pump them in their 2/90/2 poweramps, and top-line McIntosh Lab amps use these bottles in their poweramps for audio systems. Full spectrum, clear as a bell, thick range. Only thing is? They can't be pushed - unlike EL34s that get all horny and juicy when they're maxing out; KT88s will sound like asscrackers when they're pushed too hard. Good news is? The amps they're built around aren't meant to push the power section, they're relying on the preamp/tonestack stage to hone the tone, and then drive that tone through the KT88s for exacting clarity.
I'd opt for the 20thA Sheevs hands down man - maybe stick a dirt in front of it, or a clear boost (remember the CAL Mk.4:23 Pro, or regular version - they work AWESOME with the Sheevs!!) and you'll be winning. They cut, and they're versatile as hell.
I'm done
Mo