it has actually very less with ddr3 to do

i had only one i7 cpou that could do 5.1Ghz uncore
99% of them do only 4.7-4.8 and you can only achieve 2300-2400Mhz max vali

with my i7 960 i could hit 2540MHz with cas 8 and 9 too
it was uncore limited
i think your result is great but it depends more on your 32nm cpu uncore then on rams