XS's like to run hot. so if your a singal driver car you probably wont get them to the heat you want. (i run XS's)
Kumho also seems to have a bit more side wall on their tires than other companies a 45 is like standard 50. better for gearing i guess.
i hear good things about the RS3's. we should have got them last year for our STI but we ended up with dunlops and did this to them in 2 events.