Idk where you got that the grand prix is faster in the 1/4 but from the times I've seen, it's not even a close race. The times I saw for the 2005 grand prix gxp were around the low 14's (14.3 by Car & Driver). The new mustang's can do mid to high 13's(13.5 by MotorTrend). Yes the grand prix has more hp and torque but it still comes with a 4sp auto. On top of that, it's a few hundred pounds heavier.
With the vette starting at 45k and the gt at 25k, I myself would hope the vette is faster too.
I think for the price range, the gt has very few competition in terms of speed.
As for handling, just like any other muscle car, that's not the stang's strong suit. Handling though, trust me is alot better than previous generation stangs. My dad had a 04 gt and everything just feels different. Unless Lev is a autocross junkie, any of the cars would do fine I would think in terms of handling.