When you read the write ups remember the most likely to take the time to write them are people who had trouble, The tech is new and people will complain when it doesn't work the same way as their last 2 boards.
Any 32 bit operating system will only mathematically have address space for 4gig total including address space needed for add in cards like video, audio and drives. In order to use more ram you need a 64bit OS Vista or Win 7 is the one to use XP64 never had wide spread driver support.
The UD3R would not be my choice it's the direct replacement for the one you had listed earlier.
For X58 I use either this one>
http://www.newegg.com/Product/Produc...82E16813128374 or the Asus P6T Deluxe >
http://www.newegg.com/Product/Produc...82E16813131365
All though I've had a couple of issue with the Asus board it's still a good board in my opinion.
When you read the review of the UD4P the first "reviewer" obviously doesn't realize that a PCIe x1 card will work in any of the PCIe slots as they are downward compatible(a x1 card can be used in any PCIe slot x4, x8, or x16 so their really isn't an issue if you know the cards your using ahead of time research and plan accordingly as your doing.
Did I cover everything?