I believe that a foot of wheel or little more does not make
any significant difference.
However, when we have looked at video and the timeslips
from heads up races over the last 30 years = a giant 3 or 4 high
foot wheelie clearly slows the car down especially in a headwind.
Sometimes on a heads up race with everything on Kill we get them a
bit higher than I would prefer and sometimes get the 60 ft on the back
wheels. The wheelie in the video was about the max height and distance
that we like to do.
But the giant wheelies are sure fun.
However, if I eat Chinese food after 7 PM = I go
home and dream about when I did a wheelie / broke
and axle and destroyed the Tree about 10 years ago at
the Winternationals!