The OEM Regal tires, Goodyear Eagle LS P225/60R16, have the S or T speed rating:
i.e. 112 or 118 mph respectively:
The Regal is electronically governed, and at about 110 mph the gas flow stops. The weak link are the tires: I had read, that the same Regal GS sold in Europe with the better tires have the top speed limited to 220 km/h (137.5 mph). This number looks very reasonable: for GP GTP and Olds Intrigue with performance package the top speed is the same.
By the way, even lesser cars like Chevrolet Malibu are very capable to speed exceeding 100 mph.
Of course, all of this is pure theory. It would be reckless to drive so fast on the US highways.
2. Concerning the prices for Camaro/Firebird with V-8 engine:
It is easily check the prices at http://www.gmbuypower.com/
2001 Camaro Z28 starts from about $22,300, Firebird Formula - from $24,500, TransAm - from $27k. All of this are MSRP for coupe, without options. About the same price range as with Regal.
Though, it is possible to load a convertible TransAm up to almost $39k...
3. Regal GS have very good acceleration from stop. Much better than any other sedan in the price range, except GP GTP. With the same engine, transmission, and underbody, the two cars have practically the same specs.
I believe the factory specs call for T or even S rated tires for GS, so this is good enough. Any case, you probably will never drive so fast in real life. Of course, the higher rates rates give extra margin of safety in case of underinflated tires (nail, etc).
Even more important than the speed rate, though, are such things as dry and wet traction and cornering, resistance to aquaplaning, and, probably, snow traction - depending on where you live.
Next question is the resistance to the tread wear. And, last not least, ride comfort and noise. This very personal.
A lot of info you can find www.tirerack.com
See also two tires conferences on the Edmunds board: