From my knowledge (so take all this with a grain of salt)...

the i7 860/870... motherboards only have 4 ram slots on them (dual channel). The biggest ram chips about at the moment are 4gb, so thats where the i7 870 only supporting 16GB comes from (4x4).

The i7 920/930... motherboards have 6 ram slots (triple channel) so thats where the 24gb for a i7 950 comes from (6x4).

I have an i7 860 with 8gb ram and it seems fine. The furtherest I've got into that 8GB was about 4GB being used by Vue - that was for a scene with some pretty large ecosystems of imported complex meshes. Only issue I've had is a few warnings abuot running out of video memory (have a 1gb card) and having to enter a reduced display mode for ecosystem instances.

Unfortunately I haven't had access to a triple channel setup to compare my dual channel one too so can't shed any light on that. I would expect that triple channel with larger bandwidth should help a little in rendering... but not sure how much. Something that almost made me get a 920 was that with triple channel (6 slots) you can get to 12GB of ram fairly cheaply using 2gb sticks (last I looked the 4gb sticks were a bit expensive).

I ended up getting (for right reason or wrong) an 860 for its alleged reduced power/heat output over the 920 as I live in a hot house.

edit - oh, and you might want to think about a 3rd party cpu cooler. When Vue renders, it uses all the cpu cores so things might get a bit warm/hot if you leave it rendering for 10 hours.

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