As I've said on the picture on facebook (but to share also with other forum members):
To much round exhaust tips these days.
Shouldn't be to much effort to make an exhaust tip to fit the lines of the car.
I would say, left and right, rectangle with the outside following the diffuser: /==| |==\ ...hope you understand my sketch...
You have to make it part of the design, not a last minute tough "oh yeh, we still need to fix an exhaust somewhere".
Make it part of the beautiful design you already have.
Bertini GT25: Yea I got it. Kinda like a honda civic.
Koen Delvaux: yeh, but I would make it rectangle. It would create an extra dimension of wide body/low to the ground