. . . they are not british by origin and didnt really answer my question;
Nor am I, but I will try to answer anyway. Basically, what 'true' said above. From what I've read, you can't OC them an higher, and usually even less because of the VRM temps which are reportedly worse than stock. So don't go by the GPU temp reduction alone.
I got about 25mhz more than I could with stock cooling, but yes, the VRM temps are the limiting factor. (On the 1GB 6950s, VRM cooling is sub-par anyway and was likely also limiting with the stock cooler.) If I got / fabbed a massive copper heatsink that fit under the aftermarket cooler I could probably get a little more out of it.
Water would likely run you cooler, so long as you could also cool the VRMs.
Don't the full blocks from EKG cover the VRM's? I've never seen someone with additional blocks on with these and they can ramp their cores right up to 1Ghz with ease. I'm actually going to build a four card system in the near future with dual 360mm radiators for mining on. This will then be expanded to a six or possibly eight card set up with three 360mm rads and two pumps.