Nica Guy :
$850 for 2 4870 x2????
WHERE???????????
Nowhere, fuzzy math. It's around $550 each.
And quad 4870x2 is really a bad choice right now. It hardly perform above a single 4870x2, often outperformed by quad 9800gx2 for $270 each, in rare cases even by single 9800gx2. Absolutely pathetic.
http://www.hothardware.com/Articles/ATI-Radeon-HD-4870-X2--AMD-Back-On-Top/?page=9
Quad 4870x2 just doesn't have the driver support right now. Quad 9800gx2 scales similarly when it first came out, and look at it now with mature drivers:
http://www.guru3d.com/category/vga_2/
It scales relatively well for quad gpu across the board, in well scaling games like Call of Duty 4, it achieves near 100% scaling, almost doubling frame rates at some resolutions.
If history is any indication, this is a taste of how quad 4870x2 will perform after a similar amount of time. It's going to really shine, just not yet.
Get one 4870x2 now, and add another one later. Once drivers matures, you'll recognize the monster that quad 4870x2 setup is meant to be, instead of the cripple that it is now.