It's a bit hit and miss dude. The older stuff seems to do better than the newer stuff. They changed chips at some stage.
~950mhz seems to be about the average high clock, with some hitting 1Ghz and some failing to go over 900mhz at 5-5-5-15.
Yours should do 900Mhz at 4-4-4-12 @2.1v, so there should be some space for improvement.