I have been saying this here forever:
http://www.tomshardware.com/forum/265249-30-help-needed-mobo-combo
http://www.tomshardware.com/forum/263505-30-gigabyte-ex58-decreasing-problem
http://www.tomshardware.com/forum/263598-30-ddr3-1600mhz-ex58-ud4p
http://www.tomshardware.com/forum/264746-30-p55m-build-issues
Not only does Intel officially only support 1066 for the tri-channel 1366s:
SLBEQ 3.33 GHz I7-975 D0
SLBCJ 3.20 GHz I7-965 C0
SLBEU 3.20 GHz I7-960 D0
SLBEN 3.06 GHz I7-950 D0
SLBCK 2.93 GHz I7-940 C0
SLBCH 2.66 GHz I7-920 C0
SLBEJ 2.66 GHz I7-920 D0
and 1333 for the dual-channel 1366s:
SLBJG 2.93 GHz I7-870 B1
SLBJJ 2.80 GHz I7-860 N/A
SLBLC 2.66 GHz I5-750 B1
but, there appears to be no real advantage to running the memory faster:
http://www.tomshardware.com/reviews/memory-scaling-i7,2325-5.html
it just:
uses more power
makes your memory hotter and more 'stressed'
makes your CPU hotter and more 'stressed'
makes it harder to achieve long-term stability...
If you are interested in the Intel docs, I've zipped 'em up here:
http://www.mediafire.com/?yzj5ggmyt4g
The only thing that appears to matter to these platforms is
latency - and you
pay for that, buying the RAM; here's a little tool that I've been working on:
http://img513.imageshack.us/img513/7632/0137b.jpg
It 'looks at' the listed latency at whatever claimed speed, converts it to 'likely latency' at 1066 in the 'adjusted' columns, and then, in the LV (latency value) column, 'weights' the average latency for 'bang for the buck'; notice that the entire 'spread' of average latency is 4.2 counts, and the median value, 8.1 is already reached by the fourth item, the $140 F3-12800CL8T-6GBRM - at that point you are paying $15 more (12%) to get to half the available range, but to get to the other half, the price differential rises to more than double the cost of the base entry (a whopping 108% increase!)