real strange problem !

with my sistem

i7 860
p55a ud6 bios f11
gskill 2000 cl9

@ bclk di 183mhz and ram at 10x therefore 1830mhz i can set timings @ 7 8 7 20 1t, 7 8 7 24 1t and 6 8 6 24 1t

the problem is that i can't see difference in bandwith between 7 8 7 24 1t and 6 8 6 24 1t

same read, same latency with everest

why ? is it possible that memory controller limited my ram?