I've only recently started to drive in the rain but on La Sarthe and Nurburgring 24 hr course, and I find using intermediate or rain tires is much faster than Race Hard or Medium (I don't use Racing Soft for the simple fact that I find the grip is a bit too arcade like). One thing you have to make sure is to use the Real tire grip option for the "Grip Reduction on Wet Track/Track Edge" and not Low.