I would race them against other cube motored Airfix cars, really...maybe FJ, haven't tried that yet. I definitely agree that the motor would be frustrating in club meetings! Fleischmanns, for example, have slow but powerful motors and would probably outaccelerate Airfix easily.
I wonder how common it is to replace the cube powerplants nowadays? It really makes me want to keep mine untouched, out of pity for the poor vintage things.