In an autocross environment, the 315 is worth while, especially for Pro Solo and its drag strip style launch. The car was pretty successful off the line against the C5 non-Z06 Vettes. Turns were another story.
As to a 245/295 I think that would be fine save for actual tire costs. I consider street/daily driving to be a compromise at best, so I look for "cheap, rubber, and the ability to hold air" for tire purchases (plus my alignment chews up tires a bit). I saw Contis at TireRack to be a good price for DD duties rather than pay a premium for the PSS/PS2 set up. The Contis (Continental ExtremeContact DW) in a 245/265 set are $920 (plus shipping, tax, BUT road hazard is included. The PS2 are $1,602 and PSS are $1,158 with tax, shipping, road hazard extra). Yes, I am a cheap bastard. How the hell did I end up with a 1M?