memory problems on a64 m/b

while waiting for the new gigabyte k8ns m/b to tun up i was checking out various websites and im really worried because of the problems of using 2 x 512 mb ddr memory modules as it appears that if i try to use the two corsair ones ive ordered they will only run at 166 mhz instead of 200mhz but if i only use the one module that will be fine.
my question is whats better 512mb ddr at 200 or should i live with the 1 gig at 166 wil i notice any differenceby running at 166. i read toms hardware review on the 754 m/bs and that was quite alarming anyone got any views or experience on this issue..