Best mobo for 2 x hd 4850

Guys help please heres my current set up this is my old pc, Operating system:

windows xp professional x64 edition

Amd atlon 64 x2 6000 3.0ghz

Asus m2n-sli 560 sli
http://www.newegg.com/Product/Prod [...] 6813131246

4 gig 2x2 kingston ddr2 pc 800

Gecube hd 4850 512 mb
http://www.shopbot.com.au/pp-gecub [...] 16753.html

I plan to add another card to crossfire it, And change the mother board.
Now I’m planning to change the motherboard, with this motherboards
which one is better? For crossfire setting to price and performance ratio, is it worth it to get the expensive mobo or not?

1. GA-MA780G-UD3H (rev .1.0)
http://www.gigabyte.com.tw/Product [...] A780G-UD3H

2. GA-MA790X-UD4 (rev. 1.0)
http://www.gigabyte.com.tw/Product [...] ID=3002Any help would be much appreciated