I would buy as many dominoes as £56 mill will get me, then I would have 'em arranged in a straight line along one track of the Bicester - Bletchley route (perhaps on the straight stretch near Launton), because the pw is clean and generally devoid of trains.
I'd arrange for a class 108* on the parallel track. Then I'd set the two off at the same moment and see which wins.
My gut says DMU, although the dominoes will certainly build up quite a lead to begin with.
* why a 108, you ask? Well, December 1991, I rode a 6 car set - three 108/115 power trailer sets - Aylesbury to Milton Keynes and back.