I have to admit that I feel sorry for beeing rude at first. Sorry!
I'm not entirely sure if a bigger prop means much more drag in a steep-speederlike-flying-angle. The smaller props rotate so fast that that isn't a real problem but I don't know how this will behave with a much bigger prop.
Germans also played with the idea of EDF on speeders some time ago if you like to abuse google translator u can get some ideas from this thread: