Bruno Senna pitted the GT-R against the 911 Turbo in the latest episode (14x06) of Fifth Gear on a wet track. It was close, but the GT-R came out as the faster car in the end. I think the it is well worth watching the episode if you can, as it is not often you can see someone as capable as Senna put these cars in a real test and provide you with some meaningful commentary.