The CPU is a i7 920 - so i need a 1156 board - but whihc one?
The i7-920 you want takes a 1366 socketed board
Most of ones i can find, have 4 ram slots - there is no way that can be used as tri-channel for ram is there?
This is because you are looking at the wrong boards - socket 1366 have either three or six memory slots to use three-channel... The 1156 socketed boards are for the P55/H55/H57/Q57 chipsets - mostly i3 and i5...
The triple-channel memory provides mammoth memory bandwidth of 25.5 GB/s using only 1066 MHz DDR3.
In dual-channel you would achieve only 21.3 GB/s using faster 1333 MHz DDR3.
Even the next fastest (1600 MHz) speed would only match the triple-channel bandwidth, at 25.6 GB/s.
So basically, triple-channel memory @ 1066 MHz and dual-channel memory @ 1600 MHz perform the same.
Both exceed the bandwidth requirement of all the very fastest CPUs...
Which is why I run my i7 920 with triple 1066 MHz (and very tight timings).