I recall when the OEM's went roller the commonly quoted number was 15 to 20 hp gain.

Those numbers are feasible for mass production but, for the $800 to $1000 investment to convert, I've always thought more power could be found else where and still be F.A.S.T. legal.

For $1000 and just going off your signature, I'd ditch the 14's and go with 15's to increase your contact patch and you might still have money left over for fiberglass fenders.