Like all my cars, Ive run my 172 on fully synthetic oil from new - Castrol SLX when I could get it cheap (used to work for Castrol) and more recently Mobil 1. Absolutely no problem with using a 0w 40 oil, the specification of which will surpass all criteria set by the manufacturer. If a cars been used to non-synthetic or thicker oils there is a chance that you will burn more oil, but since my car has never known any difference theres been virtually no oil consumption in the first 42000 miles - never needed to top up between services.
I always reckon a car runs better on synthetic - feels a little free-er with the revs. Might free an extra horsepower or two from that pro-speed exhaust of yours CDC. Thanks for posting that information by the way - got my exhaust at the weekend but kept the existing cat.
