Heres my question:
I was planning on building my new setup with the following main parts:

Intel Core 2 Quad Q9450/ 2.66GHz/ 1333FSB
Corsair DDR3 4GB PC-10600/1333 Ram
Asus P5E3 motherboard (FSB > 1600 / 1333 / 1066 / 800 MHz)

Now from what I've been reading in this forum with all this "FSB : Ram ratio = 1:1" stuff is that because the CPU is quad pumped its real FSB is 333.

Does this mean there would be no performance losses if I were to put, say 4GB of 667MHz DDR2 Ram in with a compatible motherboard???

Because I am a little confused how this all works can we please leave this feed on stock clock speeds for now.

Thanks in advance for anyone who can shed some light on this issue

667 will be slower than 1333 although I couldn't tell you technicalities of ratios, "quad pumping" and FSBs.

FSB is quad pumped so you take the base speed and multiply by 4 when your taking about core 2 chips.

FSB=Base FSB x4
1333=333x4

The CPU speed is the base speed times the multiplier
2660mhz=333x8

The FSB speed that matter with stock speed is 1333 which means you could go as low as ddr2 667 and not have a performance loss. (assuming you dual channel the memory the 667x2=1333)

The ratio allows the memory and the CPU to stay in sync. 1:1 is ideal. but if you ram is faster it will alter it so that the effective is 1:1. (can't figure an example right now.)

Long story short. at stock speed the slowest ram you can buy is ddr2 667 and if your ram is faster then your cpu then you will not expierence a performance loss, you will just not utilize your memory to it's fullest extent.

Thanks guys for your help, does that mean that fast ram (1066 onwards) effectively only helps when over-clocking? I mean, I dont think there are any chips from Intel that would be able to utilize ram @ 1066, 1333 or even 1600 when running at their stock speeds???

mi!ez:
Yes 667 is slower then 1333. but keep in mind that memory is run in dual channel to double is speed. 667x2=1333

gtown
yes faster ram is only useful when overclocking. The next intel chip will use ddr3 and a triple memory bandwidth. So if your building now there is no real point in getting the faster memory. I would at least get ddr2 800. the extra bandwidth will help with small overclocks which are easy enough on most motherboards