We have a debate goin here in Ireland, the basis of the debate is if a dog could pull a 3 wheel rig weighing 19kg with a person on it. Some people say it's too heavy for a dog and some people say it depends on the size of the dog and the person. Most people will only let one dog pull a 2 wheeled scooter weighing about 16kg on their own.
Honestly I don't think that small a weight difference between rigs would add up to much. What may make a bigger difference in racing is how well the driver can kick the rig along vs a scooter, which would come down to design.
FWIW I did many miles with a #140 cart + yours truly (and 'petite' is NOT applicable!) using 2 med/small dogs. Walking up hills and averaging 4-5mph is to be expected, but it certainly works. I even carried a #40 bag of dog food home with that lash-up a couple times through flat city streets.
weight isn't the only factor how far ? what trail surface ? what terrain ? what type of tire
ever seen a weight pull with wheels ?
for a race a 42 lb rig would be a bit heavy for 1 dog for strength training no problem I have had dogs that pulled carts over 42lbs and me without a problem.