I've ran with the Sessantas in all sorts of weathers over the last 2 years (4 sets infact!) and never once complained about wet grip. Infact they are one of the best tyres for wet grip out there.
I drive my cars hard (well I don't this GTI but my TDI I did) and never once did I have to question my confidence with them.
The inside edge is clearly marked saying "INSIDE".
Correctly fitted the long groove that goes circularly around the tyre is on the inside.
You can see correct fitment here.