667 Mhz chips with an 800 Mhz FSB

Hello

(newbie here) ...

I have a PRECISION 470 with an 800 Mhz FSB. It has 2 single core Xeons. I'm considering upgrading to dual core chips if I can f ind them. I'm having difficulty finding any that use a 800 Mhz FSB. However, there are a few around (still only a few it would seem) that use a 667 Mhz FSB. Can I then use 667 Mhz chips in a motherboard that previously had 800 Mhz chips (I have assumed that the motherboard is somehow also set at 800 Mhz, maybe that's not correct, .... Intel E7525)? The RAM is 400 Mhz

I'm attempting to use the machine as a slave render box, so maybe a small decrease in FSB bus speed would be more than compensated for by moving from 2 to 4 cores if possible.

Thanks in advance for any input (I've tried the Intel site but it's not too clear to me)

Regards

Danny