From another POV, the wheel significance depends more on your likely average and
sustainable speeds. Aero wheels such as the trispoke are not going to offer much
if your average is down around 20-22mph, but will contribute significantly (10-30sec)
if you are 26-28mph or above. FWIW, we have found that aero bars for the captain
make about a two mph difference in bike speed between 26 and 30mph. IE that is the
drop in speed at the same cadence on the level when the pilot changes his position
from aero bars to hands on the brifters with bent elbows. If you are accustomed to
such, try mounting them on the tandem, you will find it MUCH more noticeable than
trispoke versus 40spoke wheels. If you aren't give it a try.