Just to clear up a few things.
Camaro SS from 98 on have at least 320 HP, and at most 345 HP (depending on the year) from the factory, not 310, that'd be a plain old Z28. Between a equally equiped Firehawk and a SS or a TA and a Z28, the difference would come down to driver, and what kind of engine they got from the factory (not every motor that comes off the line will perform the same).
The only Cobra I'd get would be a 2003 (if you can get one), the rest are poor attempts at muscle cars (though the 2001 was a big improvement). However, for what it'd cost you to get a 2003 Cobra, you could bot a supercharger on a SS or a Hawk and put down more then 400 HP.
Finding these cars will be another thing. If you want a new F-body (Camaro or Firebird), you'll have to scour the dealer lots for one as they are not taking orders for them anymore (at least not the V8's). Supposedly, the next gen Mustang is supposed to be out in 2004, you might try that. The rumors are flying that the F-body will be back in 2005 (depending on how the C6 is received next year).
You can't go wrong anyway you go. We need people to keep the V8 sports car tradition alive.