255/40's work great for the stock wheel. I'm running that size now and have no issues with rubbing and it has a little bit of tire hanging over the rim in case you have depth perception issues with curbs
I'd stay away from the 615's unless you're going to track them. For daily driving they aren't required. Honestly, who takes every corner at 10/10's and needs that kind of traction for daily driving? I'd prefer a good grip, wet and dry, along with good tread wear. I currently have BFG G-Force Sports on my car and they are great. Spent about $93 per tire. I've yet to break them loose with spirited driving (although I'm sure I could if I pushed them) and they get great traction in the rain. Now I won't run them in snow....they are about uselss in snow. But then again you said summer tires so there ya go
