I think (but am not 100% sure) that asus is telling you that the board will suppord DDR2 memory up to 1066, which means a FSB of 533. though i doubt you could get your cpu to run at a reasonable multiplier at 533 FSB, so it probably means that the board can detect DDR2 1066 memory and set up the appropriate memory divider. for example: you set up a memory divider of say 1:2, so that for every cpu clock cycle you would have 2 memory cycles. thus your Q6600 will run happily at its stock 266/1066 [remember, it's quad pumped] front side bus, while the memory runs twice as fast at 533/DDR2 1066 [here it's only Double Data Rate]. I was always confused by this myself, since it makes DDR3 seem kinda pointless. Who cares about DDR3 1600 if no one can get their FSB anywhere near 800mhz? But I am assured by the good people over on the system memory boardthat that IS the way things work at the moment. But it's still really confusing that a CPU requiring a 1066mhz FSB DOESN'T match up 1:1 with DDR2 1066.
But that always seemed kinda wasteful to me, so for my new C2D machine (I'm just switching over from Athlon 64 X2 now) I went with wolfdale (E8400) and DDR2- 400 memory. That should allow me to settle for a moderate CPU overclock to 400FSB/3.6ghz CPU while running the memory modules at their rated 400mhz. At least, that's the plan anyway! I won't know for sure until all the components arrive next week.
As for quad v. dual core, it's the same as the single core/dual core debate from a few years ago: Do you care more about single-threaded performance or multi-tasking efficiency. If you mostly just game (and I assume you do game from your GPU choice), then you're probably better off with dual-core. They are no slouch when it comes to normal usage and the number of games that really truly benefit from a 3rd and 4th core can be counted on one fingerless hand...
Of course, if you do lots of video-encoding, photo-shop work or other stuff that really benefit's from multi-threading, then quad core is probably better. (note that just to confuse things it's worth point out that Penryn includes SSE4 instructions which are supposed to increase video encoding performance by as much as 75-100%!)
So I guess what I'm saying is that I think the E8400 is the sweet spot right now. It's cheaper than the Q6600 (@$220 to $280), it has all the new bells and whistles (45nm process, high-k gates, 1333FSB, SSE4, 6mb L2 cache) which means it runs cooler than the older conroe/kentsfields, uses less power and is something like 4-10% faster clock for clock. There is undoubtedly a small sector of the market that should go for quad-core right now, but IMO the mainstream just isn't there yet. there just aren't enough programs that take advantage of the extra multi-threading ability.
Also, I have read at least a couple of reviews suggesting that at the upper end of it's OC envelope (4.25-4.5 ghz) the E8400 can outperform a stock Q6600 even in multi-threaded synthetic benchmarks! Now we should expect that the Intel hand-picked good chips to send to the review sites, but I've also seen a review from someone who just bought a retail box at a local store (I think that review is over at legionhardware; judge their credibility for yourself), and it reached 4ghz on air with little trouble. So unless the early indications are all universally and massively wrong the E8400 *should be*, in addition to all its other virtues, a very good overclocker.
Wow, that's kind of embarrassing as i read it. I sound like an Intel sales-person! I'm really not! In fact, up until this year I've been a pretty die-hard AMD guy. But the TLB errata on top of Phenom's rather lackluster launch has pushed me over to the intel camp. At least for now...