whats the better setup for video

[willthesshadow]

1 of these MSI R4870X2-T2D2G-OC Radeon HD 4870 X2 2GB 512-bit (256-bit x 2) GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported

or two of these crossfired POWERCOLOR AX3870X21GBD4PH Radeon HD 3870 X2 1GB 512-bit (256-bit x 2) GDDR4 PCI Express x16 HDCP Ready CrossFire

I got everything except the video card. Is this motherboard going to run it

MSI K9A2 Platinum AM2+/AM2 AMD 790FX ATX AMD Motherboard

And would you mind explaining why one setup is better

[Calum]

The 4870X2 is the better choice - the performance will be a little less but there is more upgrade room.
However I must question your decision as to whether you need to spend that amount of money.