In the wet was absolutely critical. I wouldn't be surprised the track pack GTR is on almost semi-slicks or cup tyres like MPSC. It is a little helpless on wet surface. If you're on the belgium motorway, which rains a lot, and see those GT3s/Elise/Exiges driving very very slowly that's because they're on R888/MPSC or similarly dry track tyres going to Spa/Nurburgring. They need to be this slow to keep the car stable even at motorway speed.
I was driving a Caterham R300 at Donington couple of weeks ago. There was an S-line 1.4TSI A1 (on road tyres I assume). The morning was wet and the Caterham was very tail happy, I could't get the tyres up to warm, the little water dispersion ability of a few barely road legal treads didn't help either. The little A1 passed me and took the Craners curve at very decent speed. Afternoon was dry, the A1 was still plenty fast but 180bhp/~500kg of the Caterham is a different animal when those CR500 rubber becomes sellotape sticky.