I <3 my Peavey 50/50. Well, actually, I <3ed it, until it got fried and I ditched it at the side of the road ;P
Really though, it's a great power amp with the Quad. It definitely colors the tone up like you would expect from a guitar tube power amp... just that sort of smoothing, and good chunk of natural compression, etc... I actually pretty much love EL84s, I guess. I absolutely loved my Quad ->Peavey 50/50 tone.
I started doing the road-warrior thing though, and the Peavey power amp was just not making much economical sense, particularly when you just have a little trailer and a van, and you get drunk at a lot of your shows. Not saying it's not a road-worthy unit, don't get me wrong, but after my power amp fried I switched to a QSC P/A Power Amp (though I might pick up an old Mosvalve and give it a shot when I get the opportunity) and actually, I still love the tone. Of course, the first show was brutal, but as time goes on I'm slowly dialing it in, re-EQing, and getting used to the new sound. I'm sure if I had a few hours to crank it up, alone, and tweak it I'd really love the sound. I still prefer the sound of my rig with the 50/50, but it's really differing manners of 'great.' The full-range PA power amp gives a kinda cool crispness to my dirty tones that I actually kinda like, but it sounded NASTY with my old settings ;P
I think the overall point I'd make is that with a great preamp like the Quad, and a style where the majority of your tone generation takes place before it hits the power amp, I'd consider the power section to be more of a flavoring type choice. Not that flavor is irrelevant: I know plenty of people who won't eat French Fries without Ketchup, but... I'm ranting now, and I'm going to stop. Peavey rules, solid state works pretty good with the Quad too, the Quad just rules. Done.