I am lookong to get a 1997 or a 1998 subaru impreza wrx. One is sti and the other is not, both are imports from japan. What are all the differences performance wise?

The engines are different, the STI of those years had forged pistons available. The 1998 STI had larger brakes. Depending on the STI version, it may include a DCCD 5 speed. There are also differences with the suspension, as the STI springs and struts are stiffer.

These years are not as fast as the new ones- but they are still hot- I would pick the one that looks like it was owned by a middle aged man who only opened it up on the 4th of July- just looking at the cosmetics can tell you a lot- don't get stuck with the one that has done the Paris- Dakar Rally 10 times- these things are like '60s muscle cars- the people who bought 'em raced 'em relentlessly- that's what they are for! buying a used one is sketchy- don't worry about the minor differences- find one that is still intact, if you can

Now when it comes to hp, 0-60 and top speed is there a big difference?

Top speed is the same at about 130 mph. Horsepower depends on the tune, but I believe the STI tends to be about 40 more. The STI typically also comes with a larger turbo. Which year is STI, and which is WRX? Another heads up: Those years of STI had the EJ20K, which was a very high strung motor. Running the car on something other than Japanese high octane fuel will require a retune or you will likely grenade the motor.