I had a tinkered NA Calibra XE, it was great for a second car, but ultimately a **** car. It was heavy and thus slow, but the piston slap suffered by the higher milers became an issue when I started getting oil pressure issues (Common Issue).
My 4x4 Turbo was a better car, went well, but will still ultimately the same car with the same engine just with a turbo and a dodgy transfer box to aid unreliability.
Having owned both a Rover 220 Coupé NA and a Rover 220 Coupé Turbo, I would have definitely gone for the Coupé.