Personally I feel anything that requires a Saito 150 or bigger needs gas. I would be concerned that the additional weight on a 54" WS biplane weighing 10 lb would turn it into a real dog. Carl Goldbergs or World Models Ultimate are much lighter from the start. I've a couple of 120 size 4 strokes and I do not find their fuel consumption to be prohibitive.

Just my two cents,
John