Ah, if you using old parts from the old PC, ignore what I said, I always do the same as well! My PC is full of HDD's, hehe. The SSD should be good!
The 6950 Rev 1 (If you buy one, make sure it's a REV 1 or standard design) these come with a switch that allows you to switch between two BISO's.
So even if you mess up somehow or it doesn't like it, you can flick that switch and play on with that bios or flash the broken one and try again or whatever you like.
From what I have seen, there has been 98% success rate from reading topics at XtreamSystems and Overclockers.co.uk
I brought one MSI 6950 from OC.co.uk, unlocked the shaders only by modding my own BIOS and then overclocking it to 880MHz and 1375MHz.
I seen many people OC'ing above 1000MHz and so on!
Brought a second one last night, will be doing the same when it arrives Monday or Tuesday!
I used this guide here:
http://forums.overclockers.co.uk/sho...postcount=1265 and this
http://www.techimo.com/forum/graphic...reg-entry.html