Ive superchipped my cup. Havent had it dynod yet, so dont know what the quantifyable difference is, but it feels even more responsive - more torquey. Im using 3rd far more at 40-45mph, where before i would have used 2nd to ensure I got a quick burst in. I can spin the wheels in 3rd in the wet now, too, which I couldnt before (tried lots).
I imagine that their 8-10bhp gain is an exaggeration - Im still waiting for my local RR to be fixed so I can get the facts. All I know is that I rarely drive at full throttle any more - plenty quick enough at 80%.
Oh, and its easily reversible, too, becuase its a simple flashed remap - when you get it done, they give you a memory card thingy with your original map on it, so if you get into warranty bother you can £50 to have it reflashed back to standard. I found that reassuring, but others will prefer the fact that other ECUs can handle other engine mods where the superchip map is just one fixed file.
Paid £293 inc vat & fitting at Demon Tweeks - I think the pricing is fixed by superchips.