Absolutely - with petrol engines, the S2 switch does nothing and I've always kept it in the as-shipped position. As to the S1 switch, I have it at "D" - and with RON98 fuel, never had any hiccup. As to performance gains, I described those earlier in this thread:
(
http://www.2addicts.com/forums/showp...&postcount=665).
Piotr