First eliminate bad options :
buying a used engine (too much risk),
buying an m4
that's a downgrade to a 3.0 liter engine block (If you want a proper bespoke turbo car go for a GT-R or Pturbo) and it's an ugly boring looking sedan car (even in coupe).
You safest path is a Dinan stroker. It might look expensive but think that if you replace the piston and sell car and SC it will be at a loss.
If you have deep pocket to upgrade to a porsche i would do.
I would also eliminate option of just replacing piston and keeping the car. It might be completely fine, so that just me.