will a motherboard support 1600 MHz memory if it lists...

Depending on the motherboard and CPU and whether or not you are overclocking, the 1600MHz memory should revert to whatever memory speed is manually setup in the BIOS, or default to the speed appropriate for the CPU.

i never knew the memory type was also dependent on the processor.  so which processor supports the faster 1600 memory?  i was surprised to see that the i7 950 only supports 800/1066.

here is the deal, recently (very recently last few months) Intel has been messing with the processors.
it used to be you could set the memory to 1600 on all processors without overclocking the cpu.
basically raise the QPI/uncore.
now they have locked down a few more things. such as locking the uncore @ 18 now
the uncore has to be double the memory the QPI has to be double the uncore. (thats an easy answer)
if you jack around with the Blck (up high) lower the qpi you may end up with something around 1550.

used to be you could set the ram to 1600 and the QPI to 6.4 without OCing the processor.

so to give a simple answer the best you will get on a 1156 processor thats newer without hassles is 1333

its not that simple...
all i7 1366 support 1600
all older 1156 support 1600
(regardless of what intels website says)

what intel has done lately is to stop easy overclocking
if you buy the 875 which is unlocked rather than the 870 (same default speed) you most certainly can set ram to 1600

this is not the first time Intel has done this.

so 1600Mhz memory for say an i7 870 is pointless?  No way to overclock that 1333Mhz memory to a higher speed? 

I don't want to pick up a pair of 1600 memory for my 870 build if it will lock up.  But is it still possible to use that memory to take advantage of the timing speeds?  ie. 8-8-8-24 and hope that the CPU will downgrade the speed to 1333.