Oh boy, the ship is almost completely submerged, but you're still clinging to it, apparently by choice. There's a life raft right over here fellas ... It's called the USS Common Sense!
Ok, didn't really think this would be necessary because common sense should've been all that was needed, but imagine this:
A customer wants you to move, spread, and fine-grade 80 yards of topsoil. You can choose gear trans (old gear, shuttle, PS... Your choice) or HST. But the machines will be identical in every way besides trans. And, your skill level will be the same because you've got a zillion hours of experience on both tractors with their different transmissions. So now, all things are equal.
If you're being honest, and have had experience using both types of transmissions, which tractor will be more efficient at the task? It's obvious that HST will. Skills have nothing to do with which one is better FOR THAT JOB.
All things are never equal. But my answer to your question might surprise you a bit because between a power reverse and a HST it really would be which ever machine is closest to the trailer. The job will be finished in almost the same amount of time if there is no distance to move the topsoil but if the topsoil is dumped at say the roadside even an 1/8 mile away from where it needs spread and graded then I would walk the extra distance to get the shuttle and take it over the HST.