The biggest factor from the wind point of view, is not the bike but the
riders. Tandems have twice the 'sail area' that singletons do and in
anything other than a straight head or tail wind the increased surface
area contributed by two riders will be much more than any minor
contributions from changes such as you mention. Trail on the fork
will have some effect on handling but not as much as you want.
Spoke area will not be enough different in the sizes cited. This assumes
a typical wind, ie less than 10-15mph normal to the bike.
Gusts and higher winds will have effects that go up with the 3d power
of the wind velocity IIRC.