I like the AMD R9 RAM for ease, at least on the Sabertooth set AMP profile in BIOS and all is done
I got the R9-2400MHZ Ram for my latest build, but only becasue it was actually chaper than the 2133MHZ RAM in the UK when I got it.
Mine runs rock solid at 2400 MHZ but it will default back to JEDEC SPEC of 1866MHZ if there are issues, and I have to be honest and say I don't know how other users milage with RAM faster than 1866MHZ and FX chips is.
I have also not done tests on difference between 1866 and 2400 on bench marks, but since it runs at rated spec on the AMP profile and is rock solid stable no need to slow it down
System - Runs Cool and 100% Stable
AMD FX 8350 @ 4/4.2GHZ, Corsair H60, ASUS Sabertooth 990FX R 2.0, 8GB AMD R9 2400 MHZ RAM, 3GB AMD R9 280 GPU, Crucial 240GB M500 SSD, Seagate 1TB SSHD. housed in a Corsair Carbide 300R Case with Corsair CXM 750W 80+ PSU