965 mobo: more capacity or more mhz?

hi,
there is one old and (quite) smoothly running machine built around intel's DP965LT motherboard. which i would like to upgrade with more ram, but there's a question rising up...

the chipset have 8gb memory limit. it can use 800 and 667 mhz sticks - up to 4gb it can use 800mhz, but in case of 8gb there must be 667mhz sticks used. there are now four 800mhz sticks on the board, counting 4gb (correctly, 3.2 on 32bit win xp).

now, if i upgrade to 8gb (windows always like that), the ram will operate at 667mhz so the main question now is; what have more sense - double capacity at 667mhz or leave the same capacity at 800mhz?

present stick now runs at 5-5-5.

thanks in advance!

also 32 bit operating systems like yours don't support more than 4 gigs of ram. also 4 gigs is plenty