An update on what I did. I have the 16x8 fronts and 17x11 rear wheels. My existing fronts were 225/50/ZR16 and rears were 315/35/ZR17. I could only get a finger between the rears and mufflers so couldn't go to 335 size. Couldn't find sets of 225 front and 315 for rear. I switched to 285/40/ZR17 for rears which are slightly bigger diameter but narrower. I could only find these sizes as sets in Continental and Pirelli P-Zero. I bought the Pirelli P-Zeros as listed in the Tire Rack P-Zero System. They are Asimmetrico. The fronts are listed as N3(Porsche) for 8" rims. Both UTGs are 140AA.
I have installed the new tires (actually bought thru my local Tire Factory store). They are fine. The rears, although narrower tread width, look great, maybe better.
Hope this update for these sizes helps someone.
Thanks for all your help with info.