I'm new to this whole mining thing and I want to setup a little rig. I've been eyeing up some cards I want to purchase and need help deciding which one is better / more worth me buying...

I'm going to purchase 2 cards and I will be installing it in an Asus P8P67 REV3 with a i5 2500k.

Board: http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2004774&CatId=13
CPU: http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=7073161&CatId=6988

Card 1: $259.99 -$30 Rebate = $229.99
XFX Radeon HD 6950 http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=708648

Card 2: $259.99
Diamond Radeon HD 6950 http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1387558

Card 3: $183.99 - $10 Rebate = $173.99
Sapphire Radeon HD 6870 http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1006280&CatId=3669