So just tried a shifter kart arcade race on Silverstone in 100% weather, with 100% surface water and real grip.
You certainly remember that the karts are on slick tires, that's for sure. The shifter wheelspins constantly, can barely drive straight and will not turn without throttle. You can mash the gas however, and with a little countersteer, slide all the way through and out of the corners. Lots of fun, but it does seem to break the AI though. On turn 4, half of the field just stops and waits for a few seconds and then slowly start moving.
It was taking me nearly 4 minutes to lap the GP circuit!