I would go with the GIGABYTE GA-X58A-UD3R Intel X58 Socket 1366 ATX Motherboard or the ASUS P6X58D Premium. And I would go with 6 or 12 GB's of triple channel memory instead of 4 GB's of double channel. Pick the better board for you and we'll help with memory.
Your i7 is on the 1136 platform, which has triple channel memory, id get a 3x2GB ram kit.
Have you brought the parts yet? Get a single GTX 580 now (or wait two weeks for the 69xx series to launch and see what happens) and SLI later...
Get the HX-850, build will be neater and more efficent.
No... I would go with the ASUS P6X58D-E or ASUS SABERTOOTH X58 before the UD3R. If you have a little higher budget, I would look at the EVGA X58 FTW3.
As the group mentioned, you want 6GB (3x2GB) DDR3 for an X58 board, however, it isn't a must. You can run with 4GB (2x2GB) DDR3 in dual-channel mode on most X58 boards (just not typically recommended ).
edit: As for your build, I give you 5.5 with your current choice of UD3R & 4GB of RAM.
I like the UD3R because it has so many sata ports, never had driver issues or component failures and overclocks nicely if/when you get around to it. It's a little on the older side but there's a reason they still sell well. even Newegg still sells them and they are quick to deactivate items that don't sell well. Shoot, I use it on one of my favorite builds as you can see in my sig. So yeah, to me that's a viable option that rates at least a 9. I'm not trashing the asus board, the premium board is good also (one of my recommendations). But I have first hand experience with the gigabyte and it's great.