Please Give Advise!!!!!

[Stuart]

Need to buy new wheels for my porsche boxter rims(7x17 and 8,5x17). On the front i'm thinking of 205/40/17 but for the rear I really need advice!!!! I've porsche alloy arms and 944 turbo brakes on the rear. What is the tyre to buy? 205/215/225 or 235? Can i go also with 205's on the rear because I can buy a set of Toyo's for a very good price. Come on everybothy, tell me what your are thinking or what your experiences are. Greetings from Holland.