Agree with terayon. The BMW can is supposed to be quite free flowing anyway, it's junking the cat that significantly improves the breathing.
As for tyres, it's often a subjective thing but I'm now running Michelin Pilot 2which are great in the wet, dry and have already lasted longer than the usual 8-10k rear 12-15k front I'd get from say Anakee's. Never tried Bridgestone for comparison but I'd never go back to a trail tyre, especially as I never go offroad!