My bike was already fitted with a Scorpian can when I bought it so I can't really compair it to the standard OEM can, however when I took the DB killer out it did seem to run better than with it in, forgot to put it back in for the MOT on monday but it still passed.
A mate of mine mentioned that if you put a different can on and it runs a bit shit, to get it jetted, not sure what that means, involves or costs but it's 'allegedly' ment to be really good for it.