New system, could use some advice!

Howdy folks,

I've recently bought myself a Powercolor HD6950 PCS++ GPU. Great, except for on thing. It's plugged into an old LGA775 board. Ouch indeed.

So, I'm looking to get myself a new system, based on Intel's Sandy Bridge. Particularly, I'll be looking to go for an i7 2600k.

Now I love me some graphics grunt, so in future, I'll be looking to add another graphics card to this system. Unfortunately for me, the PCS++ I have is quite a rare beast apparently. When they were released, they flew off the shelves, and now AMD has put a stop to the shader unlocking goodness. Will I be able to run another HD6950 in Crossfire, or does it need to be exactly the same one?

Regarding the motherboard:

Sandy Bridge: P67, or Z68. From what I understand (PC Format ftw) the Z68 combines the on-die GPU and overclocking ability. Now that I'll be using my own GPU, is it worth the extra premium for the Z68?

With that in mind, and the fact I would like a Crossfire setup, which mobo would you guys recommend? I don't need gold plated contacts or time-warp switches, all I want is some decent overclocking, crossfire support, USB3, and all the usual run of the mill stuff.

I'll have more questions as I draw closer to the purchase date, but this is something to start off with.

Cheers in advance!