A friend of mine ran turbo 19x11 rear wheels on his '98 Boxster. He had to roll his fenders and used spacers but they did fit.
Although it can be done, unless you have wads of cash, I'd advise against it simply because of the cost of tires could put one in the poor house.....IMHO I think 18's are the sweet spot for looks and tire cost and choice.
Plus, you can use the money you saved from not having to purchase 19" tires and lower your car making the 18's look even better and probably have some $$$ left over for the other mods you will eventually end up doing....
