Interesting choices.

Repairs on the foreign cars will be expensive compared to the Mustang.

V8 with stock exhaust won't be pony boy loud, unless you have a GT350 or 500 with a more performance oriented powertrain. Then again, the AMG's I've driven have a louder exhaust note with the AMG exhaust than stock Mercedes.

Mustang with the Ecoboost will be cranking out 300 HP, more than the old 5.0 Ice Ice Baby year mustangs and they were considered quick and would get better gas mileage and still have plenty of power.

I'd prefer a sportscar. Here is my first......way back in 1967. 350/327 M20 3.36 gears Marlboro Maroon Roadster.

Dang, now I'm looking up first gen SLKs.
There's a SLK32AMG here in Houston for <$10k, but it's got high miles & a matte paint job.