I have a 3930K and Quadro 4000 on Mavericks right now.
Power managment is getting better all the time on the SB-E CPU side, with 10.9, it's almost there, some reports say it's fully native in 10.9.2. But if you're building a new system, get the newer IB-E CPU, it'll be better supported in the future as it's the same architecture as the new MP's are running on. Read up on some x79 guides and go with the 4820K. If you can spare the cash, also seriously consider the 4930K, the two extra cores will help.
As for old vs new Quadro, the old one requires GE=Yes and some kext edits to get power management working. It's based on the GTX 400 series and it also runs seriously hot. The newer one is more powerful, based on the GTX 600 series, so in theory should be able to boot without GE=Yes and should have better support overall. Although that's only speculation based on what we've heard about cards like the GTX 680.
I was considering getting the K4000 a few weeks back, but shyed away because of the massive price tag. The downside is that you can get a 4000 used for a few hundred bucks, whereas a new K4000 costs the better part of a grand.