I think that "by BHP" way is more accurate.
Bike exhausts are usually less restrictive and louder... especially racing cans - exhaust pipe diameter is larger than standard Zetec.
Another "pro" thing is that CBR revs to 13000rpm and Zetec max. rpm are about 7000... so even 600cc bike engine produce lot of exhaust gases...
For me - this should be OK
