If I had to choose between faster render times or faster manipulations in the Pose room I would choose the latter.  So for me a good video card is much more important than a faster CPU.  My machine just has a GTX760, but that's enough that I don't think I've encountered any lag at all in the Pose room, even with big scenes.  I've had lower end video cards in the past that just drove me crazy because it was so laggy in the Pose room when working with a busy scene.