Whew, good catch! I almost got the IDE version on accident.
I was thinking I'd go with the stock heatsink since I'm not planning on doing an OC, but for an extra $30-40 it's probably not a bad idea. I just hope that XIGMATEK fits in the Antec 300 (people say that it does, but I bet it's just as tight as they say..)
So what makes those mobos better for CrossFire out of curiosity?
"Being an X58 board, the two 16x PCI-E lanes provide 16 lanes of bandwidth to two ATI graphics cards simultaneously for your CrossFire pleasure. However, unlike pricier X58 boards, the UD3R is not officially compatible with Nvidia's SLI, although by flashing the BIOS with the Gigabyte GA-EX58-UD3R-SLI it can be enabled because the hardware is essentially the same. The same goes for the MSI X58 Pro and X58 Pro SLI as well. "
Now that's good to know. I was leaning towards the 4870 for performance reasons, but $20 less for the GTX 260 (and the fact that I'd get to play around with CUDA) are deal-makers I think. And since the board actually supports SLI, I think that just about seals the deal.
Funny that the UD3R-SLI costs about $25 more (if you include rebates)...