A stock 99 Cobra Vert will smoke a stock GT vert of similar year from a stop...... If you learn to launch with the IRS (wheel hop) or get the parts to control it. From a roll, it is no race, especially with 4.10 gears in the Cobra. It really likes to rev- I went from a 5.0 GT to the Cobra, had to learn to keep it above 4K, where it really screams.
If you do get a convertible, first thing I would do is get a good subframe set, preferably with some form of cross braces. Being a vert owner you well know the shortcomings (cowl shake) of those year verts. I've got the Kenny Brown Extreme package (Subs, x-braces, strut tower and K-member brace). Installed 3 weeks after I bought it and made a huge difference even when it was pretty stiff still.