Firstly whats your location and budget? We can suggest a few good exhaust shops.

IMO, I'd go for a custom 2" or 2.25" mandrel bent mild steel exhaust, hi flow cat, one or two resonators and a twin loop/oval muffler or something restrictive.
Performance wise wouldn't be much, but it'll feel slightly better in the high rpm range.

I'd suggest pairing the exhaust with a good air filter setup with cold air feed and those electronic throttle controllers for better response.