go with whatever bike size fits you.
bigger wheels are not necessarily faster, it's the weight of the
bike and the tires that makes the difference.
(i read an article in bicycling magazine in the 80's i think
that proved 24" wheels were the "fastest" for road bikes...
something about optimal reduced rotational mass maybe.)

Fact or Fiction? Big Wheels = Fast Wheels?

i've pulled a bob many miles with both 700 and 26. as far as my
untrained memory recalls, no real speed difference that could
not be traced back to how much gear in the trailer, and what
type tires.

get the 26 with some 1.5 slicks.