What is the better choice in terms of cpu fsb and ram speeds?

Ive been researching a bit about ram and fsb relationships and it seems that to get good performance, the fsb and ram has to have a good ratio like 1:1 in terms of mhz. if this is the case, will it do any harm to use an 800mhz fsb with 667mhz ddr2 ram? or stick with a 667 mhz fbs to keep a 1:1 ratio with the ram? (uming i use a cpu with same ghz, same L2 cache, etc, just different fsb)