m-spec is pritty much the same, has better brakes and side skirts i believe. If you wanted to build an engine an rb30det would be a great one to build up, far more power and more importantly more torque out of one of those than you could ever dream of mustering up out of an rb20.I my self have an rb20, at the moment have around 140 at the wheels, looking to get 200 by the time i'm finished. You should really consider building up an rb30det, there are loads of people here doing it so your never more than a question away from your answer. Cheers, now that you've been bitten there's no going back!!