800mhz may be faster but will the entire computer bottleneck.
thehoff, I think the whole 1:1 thing is more often thought of when overclocking, it is sometimes better to have the RAM and CPU in a 1:1 ratio for performance/stability when overclocking. Using 800Mhz RAM WILL NOT give you a bottleneck compared to 667Mhz RAM and it will certainly not be less stable on that motherboard, IMO. In fact, many enthusiasts would not even consider purchasing 667Mhz RAM today and the 800Mhz RAM may or may not feel subjectively faster to you.
For instance, if I have DDR2-800 that the mfr. rates as stable @ 1066Mhz I can run it at 1066Mhz and I may see some performance benefits in doing so (so long as my motherboard can handle that), whether I'm @ 1:1 ratio or not. Now, my Northbridge is going to have to run a little harder to support that 1066Mhz. ...but 800Mhz DDR2 RAM (a JEDEC standard) is so easy for contemporary chipsets that there's just no reason/benefit to run anything slower.
There is more to it but for brevity sake....