Well whats more important to you getting a decent time or having your $60 tires last a tad longer? Making a few passes on them won't shorten their life span to much.

The way I see it is, why race if your not going to give it your all? that would be like swapping motors from a d15 to a b18c and shifting at 4,500rpm when racing, or adding a turbo and only running 2.5psi when you've had it tuned for 10psi.
If you want to be able to say that you've run your car on the track and have an excuse for a crappy time then run the 185's, if you want to run your car on the track and get the most traction and possibly a better time then run the 205's. Granted there isn't going to be a day and night difference, but every little bit helps. The difference may only be that of adding a cai or header, but it's a difference.