A couple of things you are asking about have been discussed a lot:
1. Will you fit?
2. Thoughts on the SRT6 vs. GTO.
If you do a bit of searching, you'll find all you want to know.

Had they made the GTO in a convertible - I would have probably bought one.
Each car has their pros and cons.
Handling - SRT6.
Back seat -GTO.
Less expensive mods - GTO.
Etc.

Good luck.