if the bios doesnt regulate the vrms for 45nm youre screwed, not sure what node the 6600 is voltage is key. Huge reason I dont buy established brand premades is the fact that you dont know what TDP the socket is capable of or what the bios can do for VRM with an update.
you should be speaking to dell and not the front office idiots that speak from a manual, best bet is forum surfing for others doing the same