I don't know the answer in terms of games, because I don't know how most games access the RAM, but in terms of bandwidth ddr3-1600 >> ddr2-800. The ddr3 would never perform worse, unless I'm confused. http://en.wikipedia.org/wiki/CAS_Latency
Their latency (the time to get the first bit) would be identical, but the higher bandwidths of the ddr3 would send data at a much greater rate. A well designed program should therefore take advantage of this by reading clumps of data from RAM rather than scattered bits of data all over.
The questions that I don't know the answer to is "how much does increasing RAM speed affect game performance?" and "how well are games programmed to take advantage of fast RAM". My guess (unsubstantiated, mostly), is that in terms of FPS, there will be little difference using either of these on a Intel c2d, as the large L2 caches seem to make them relatively resistant to increasing RAM speeds.
Latency is not the same. I can get DDR2 CAS 3 vs DDR3 CAS 7. From what I've read DDR3 doesn't become faster until DDR3-1600 speeds. DDR3-1067 and DDR3-1333 are slower than fast DDR2 ram. What about amount thrown into the mix? here's my dilema:
I am pretty much wondering the exact same thing! Should I go with a motherboard that accepts a 1600 FSB and go for 1600 DDR3 at CL7 or do I go for a motherboard with 1333 FSB and get double the ram at 800+ CL4?
It's a real dilemna for now, as both seem to be almost identical, the only thing is that I wouldn't be able to upgrade the speed of the ram, seeing that at 1600 DDR3 is already at max of what today's mobo's can take, I could only wait for lower latency ram to replace the CL7... is it worth it? or should I go for lower latency DDR2 and maybe next year just replace the mobo and ram???