I haven't found too much of a difference with either colour pair. For 2GB sticks I found the farther pair (a2/b2) to be a little more tolerant to clocking high. For 1GB sticks it didn't really matter. Which revision are your corsair dominators? It says on the dimm, ie. rev1.2, rev4.1 etc and what capacity are they?

I've clocked two different pairs of 1GB dominators on this board, rev1.2 which are micron ic based and they gave me no problems at all clocking all the way to 1240mhz at 5-5-5-18, then another pair of rev5.1 which i believe are elpida based ics and they were complete garbage they werent even stable at 1120mhz no matter the timings or voltage.