Both of your cars can handle 450HP no problem. More like 450RWHP!!! Safe tune and good gas is all you need. I have been trouble free for 10,000 supercharged miles.
95 Cobra. I would buy a nice Edelbrock H/C/I package. Good headers, Prochamber H-pipe, an Flowmaster cat-back exhaust. This car will sound awesome!! In the future, I would suggest a Vortech S-trim with 8-10 pounds of boost and see where you stand. If you want more, go with 12-14 lbs and a good methanol injection kit to cool inlet temps and add increase octane so you don't have to run race gas.
03 GT. Looks like your GT runs good already, I didn't read you entire sig, just your 13.38 time. That is pretty fast for a midly modded 2V.