Building a new workstation/gaming rig

I'm currently planning to build myself a new home workstation/gaming rig and I've been shopping around for motherboards that fit my requirements(mostly in terms of offering more than two 16x PCIe slots).

From what I've managed to gather without buying a barebonesystem ASUS's P6T7 WS SuperComputer mobo seems to be the choice for me. However as I am looking for a all purpose machine which includes gaming I'm also looking at overclocking.

Now has anyone had any experience with overclocking on this board? Is it any worse than one of the purpose built cards on the market in terms of settings etc? I'm also looking at thermal profile as it will be used in a home environment.

Just to iron out the basic specs I'm currently looking at starting off with the following

i7 920
12GB RAM 6x 2GB modules(make a model is still open)
2x 4890s or alternatively 2x GTX 275s