Having driven both cars, I'd concur that the 997 is faster with a more compliant suspension. It also has electronic gadgetry that the 996 does not. The 996 seems a bit less refined in both suspension and power. I'd take the 997 in a heartbeat. Either way, they both need safety gear and suspension work. It took me about a year of track driving to lose my fear of my 996 GT3 and it's power-on oversteer tendency. There are a lot of GT3's with damaged rear-ends. It's easy to apply too much gas on corner exit, and the rear is unforgiving. It is not a comfortable car on the street. If you look around, there are a lot of very low mileage GT3's available, I think because of the comfort issue. The 997S has more torque and is probably a better street/canyon car.
Performance wise, I've been beat at Fontana twice by less than a second by a similarly prepared 997 GT3, both on Hoosiers. I like to think he has been a better driver, and I'll get him this year. We were both beat by the Duncan's Koni Challenge car and Steve Eguina's GT2, so either way, you'll be in good company.
All that said, can you think of a better deal than a mid $50's 996 GT3 or a mid $70's 997 GT3 with a crazy great motor and most of the suspension goodies you'll need? Remember, it is the track version of the 911, and it will be happiest there.
I'll be happy to give you a ride.
