Here's a second to Randy's suggestions.
My current street setup:
- 195/205 width tires front/rear (AVS Intermediates)
- Max negative camber all around with Dot2 crash bolts up front (about -2 degrees in the front)
- Slight toe out in front, neutral toe in the rear
- Saner 1" front swaybar (you can find stiffer) set to stiffest setting (very easy install)
- Koni Yellow strut inserts that I installed myself in an afternoon. Note: I am not a dab hand with car work and while this installation was nerve wracking it really wasn't hard.
For autocross I run in C stock and I currently have ~8 year old Hoosiers in 225 width all around. They had been sitting around and were unscuffed until my first event on them last month.
When I first put the AVS 195s on the front the car did feel a bit different (I had not yet put in the swaybar or the Konis). Soon after the tire change I spun the car on the highway when cut off at 80 mph but was lucky to have nothing worse than a scrape on my bumper from it. While the car's balance was somewhat changed by the wider front tires I believe the spin was more my fault than the car's (duh...don't lift and jerk the wheel at the same time...I was tired, that's my excuse and I'm sticking with it). The car handles significantly better now with the swaybar, Konis and alignment and has nice balance throughout a corner. With the current setup in the car I believe the likelihood of a spin in the same 80mph highway conditions is lessened although I haven't tried it again.
I have only autocrossed the car once with the 225s all around and I was very happy with it and had zero spins.
So, the car is still drivable with same sized tires on it although you may notice some changes in the balance that can be dealt with both with improved driver input and some suspension tweaking.
As for trying to get better times...you can do that regardless of the tires and setup. I didn't have this car even close to well set up for the first 3 years I autocrossed it (it still isn't really very close to the best C stock allows). On a few occasions I have had a friend who has won a national autocross title drive the car and he has thrown down faster times than people in much better prepared cars. Of course it is good to improve the car if it is hindering you, but don't forget that the most important improvement you can make is in your driving.