They are mixed rather evenly, we won 8 features last year with the 602, have won 5 so far this year with the 604. They seem not to make much difference. It's more of a weight preference, if your over 250( unless you have a fairly newer lightweight car) better go with 604. If not, I would recommend the 602. They seem to be more durable engines, less cost, easier resale if you want to switch.