"All told, it is a much cleaner and better-performing solution than its predecessors."
I object to the introduction of facts not in evidence. I haven't heard anyone claim that Intel + GEM graphics performance is better than the way it was before. My experience and the experience of pretty much every user posting to the xorg mailing list is that the latest bits are a noticeable regression. The problem is finding what caused the regression. Is UXA worse than EXA? Are they both worse than XAA? Is GEM busted? Nobody can tell.