Out of the budget range, David.
The Asus is more expensive for a reason - Biostar boards are okay but they are not top quality.
There are only so many PCI-E lanes to go around on P67 and Z68 boards. All the boards will run the primary slot at 16x, but what happens when you add a 2nd card varies depending on the board. The cheaper ones generally will keep the primary slot at 16x and run the 2nd slot at 4x. The better boards will run them both at 8x. The real high end boards (such as the Revolution) can run them both at x16 because they have an addon NF200 controller.
When you Crossfire, 8x/8x is preferable to 16x/4x.
I personally don't think Crossfire is worth it, it overly complicates things. A 6950 is a very strong card by itself. Board and PSU for a single card:
Newegg.com - ASUS P8Z68-V LE LGA 1155 Intel Z68 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard with UEFI BIOS
Newegg.com - Antec EarthWatts EA-650 GREEN 650W ATX12V v2.3 SLI Ready CrossFire Certified 80 PLUS BRONZE Certified Active PFC Power Supply