I think there is some more potential left in the 1.5L diesel / Rampage combination. More fuel, more boost, better flow through the head, more gear/tire..... Keep adding these together until something lets go.
My current daydreaming bounces back and forth between trying to wring more out of the current combination, and building another engine to put in the Rampage for a different class.
I already have a pretty fair collection of parts to build a bigger engine, and have the "hookup" for both diesel and gasoline possibilities.
It doesn't cost anything to dream, but once you start buying parts, the $$$$ add up in a hurry.
Right now, my credit card is busy recovering from this adventure.
Steve