I never had the R888s in the these sorts of conditions on track, only dry tracks and they were brilliant.
Honestly they were shocking and quite well worn, so not a great comparison. Conditions wise, Brands was a lot worse than Silverstone and the GTR was losing traction and sideways constantly, ended up switching the traction control off and turning the boost down. It was great fun, but slow as hell!!! A lot of that is down to the weight and power of the car, I run something like 285 and 315 tyres it was just hilarious!