As an owner of G.Skill RipJaw Z 2133mhz CL9 ram (on a R4E & SB-E 3930K platform)
The ram is very nice, though i have noticed even using the XMP settings it does get a little picky on settings at 2133 speeds. Its nice seeing it run at 2133 speed but was hardly an improvement in performance over 1600 speed
I'm using 16GB of g.skills at cas:7-8-7 1600mhz. Everything runs fine in ultra (BF3).
Also your CPU and other hardware have to be able to run at certain speeds in order to take full advantage of the 2000+mhz.
(I think, it was explained to me a while ago but memory just isnt working well )