LCD panels can only display resolutions within their boundaries without artifacts. Unless you're talking about displaying at full screen.
Basically, an LCD panel rated for 1280x1024px can display 1024x768 just fine without any artifacts, as long as it's not at full screen. [/obvious]
However...
If you're connecting two fans to one header, then I'd be worried about the fans running at really low RPMs due to a lack of power.
But only 4 pin headers have PWM control. The three pin headers will only report rpms.
However, if you only want to use one header, I'd suggest getting a Y adapter...
I don't have the cash for the 5800 series, but the 5000 series in general is pretty impressive. I've been thinking about picking up a 5770, though probably after the prices drop a bit.
But then again, I'll also probably be running linux on the machine I'd put the card in, so Nvidia would...
I remember when 4GB of DDR2 was under $50 around springtime last year. Glad I bought that when I did.
Too bad I didn't know I'd be getting a P55 board at the end of the year, or I'd have gotten some DDR3 as well.
Judging by the descriptions, it seems to me like one of them is designed to run quieter than the other. Though I imagine the manufacturer's part number would vary between the two models.
But seeing as one has a higher memory clock (and assuming that wasn't a typo on the website you found it...