If you want more info on 3si cars check out
www.3si.org. Get on the message board and talk to people who really know about these cars. I have had my 91 Stealth R/T (same as a 3000GT SL) for almost two years now and it has been good and bad. These cars are pretty heavy but pack a lot of power under the hood for the price. SL models are 222hp and the VR-4 are 300hp up until about 98 or so when they upped them to 350hp. If you are really serious about getting one of these cars and are looking to keep it for a while I would say spend the extra cash and get the VR-4 or Stealth TT. You can do tons more mods and your car will haul ass.
Here are some more good sites for 3SI lovers:
http://www.gtpro.com/
http://www.stealth316.com