It obviously depends on how much loud you wanna go.
If we can put down a ranking based on decibels, it should be like the following:
- Full exhaust with decat, de-opf, free center pipe, only light silencer at the back
- Full exhaust with decat, de-opf, light silencer at the center and back
- Sport cat, de-opf, free center pipe, light silencer at the back (similar to Ragazzon)
- Sport cat, de-opf, catback RS exhaust
- Modify original downpipe to remove OPF and leave everything else stock
I'm in for the number 4 'cause I think it would be already a great improvement overall in sound and temperatures.
Cost wise should also be the cheaper way considering that a good catted downpipe should be around 8-900£ and will be plug and play with possibility to rollback to stock easily.