i'm currently running a rb26 (built) with single gt35R with a TRUST cartridge and she get full bost at about 3200rpm and winds out to 9000rpm, appart from the associated power hikes and all, the rb26 at full tilt at big revs is something ppls have to listen to once in awhile. if 300kw is ur goal get a rb26 as a rb25 would be straining it and the last thing u want is a car in the workshop most of it life.