The furthest you will be able to go with 800mhz memory is 400FSB, as 2.0x is the minimum multiplier for DDR memory. As such, you will be limited to 3.6Ghz with a Q6600 (no big issue, as Q6600s can't often get that far anyway), or 3.2Ghz with a Q9400 (a big problem, Q9400s can go much further than that)
I'd recommend you spend the extra for PC8500 and a Q9400, as the Q9400 is the much faster chip. This is what I recommend you get:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820145214
Thanks I'll think on it. the 3.6GHz (not expecting to get that far) sounds pretty good but how high could I possibly get the q9400 with the PC8500 RAM?
That's correct, 1066mhz memory due to the way it is constructed does not overclock very well at all, but it doesn't need to. You can overclock a system to the max with it. The only possible CPU 1066 RAM isn't enough for is a QX9770, as it will be limited to 4.26Ghz (only, haha), and since the QX9770 is an absolute fortune anyway, you'll be fine. In reality, 533FSB for a motherboard to achieve is very rare with any Quad core, usually they top out at 505 anyway.
The EP45-UD3P is a good board, especially for overclocking Quads. Crossfire is up to you really. I never approved of the 'one now, crossfire later' approach as usually by the time you buy the second card, it would be no more expensive to take the old card out and put a new single one in. The only reason I did it is that nothing has yet eclipsed the HD4870X2 despite it having been out for 8 months...
