While in Switz, stick to the rules, it's not worth pushing your luck!
You
must have a motorway pass if you use them at all. You can get them at the border or at petrol stations (or at the Swiss tourist office in London if you happen to be passing!). On the spot steep fines for not having one.
Speed limit is 80kph on normal roads, again, on the spots for speeding and the fines get
very steep as the speed increases!!!
Apparently they can be sniffy about foreign sat-navs, you're not allowed speed camera databases (they can confiscate).
Aug/Sept the weather can be very hot or very wet, as others say. Mountain thunderstorms are monsters.
Lovely country though.