well every 110-120 lbs equals one tenth off your times but rotating mass is different, for simplification every 1lb of rotating mass = 10 dead weight lbs.
go find out how heavy your new rims are with tires and then subtract that from your stock rims with tires remember you have 4 rims and tires to add up and take that value and see what it is, every 12-15 lbs will be a tenth slower~
So what would you recomend buy for a stock v6 which my future plans are mac long tubes, mac high flow cats, mac exhaust system with 2 1/2 inche pipe, and a straight air shot air intake? I would think 17x8 sounds reasonable.
I think i will get 17s. My brother has 17x9s on his mustang and they look nice and plus he lowered his car by custom cuting his stock springs. His car has like a 2 finger gap between tire and body for car. This picture is before he lowered his car.