Years ago when I was looking for an XR4i, I had a test drive of one that had been fitted with the Power Engineering Sprintex charger. That charger was originally off one of the XR4x4 conversions they did but he had bought all the kit and fitted it to the rwd V6.
Was a really nice car - I would have bought it if the guy who'd seen it an hour before hadn't had first refusal. They come up now and then for sale. I think it was about 230-240bhp.
Derek Bell, the racing driver, used to have the 4wd version and reckoned it was one of the best cross-country cars he ever had.
I've just got the wife's Cooper S to have a go in now - doesn't have the nice soundtrack of the V6 though