If you can accept a few assumptions, it is easy to calculate. First, assume the 139 yards (40'x40'x27" deep approx), 150 foot travel, 1/5 yard BX bucket, versus 3/4 yard skid steer bucket (60" bucket), 3 mph travel speed, 20sec load, and 10sec unload. It would take roughly 19 hours with the BX and just over 5 hours with the skid steer to move the material. These are fairly conservative load/unload times for even an inexperienced operator, I think, though I must admit not having much time at all on a bx. I know I can do it with a
B7510 and they are very easy to accomplish with a skidsteer if all you are doing is loading, transporting, and dumping. Three mph is walk speed so that should be fairly easy to accomplish even slowing for some part of the trip. The hardest question to answer from afar is whether a 60" bucket would clear everywhere. Also be sure the concrete is thick enough to support the skid steer and load. The rental company can tell you the approximate load footprint of the skid steer. If the bx cannot average 3mph, and 30 sec load/unload, the spread gets greater.
Next analysis using the approximate hours for each, would be to determine rental and delivery cost of a skid steer, plus operator cost, then compare that to total cost of operator plus bx for the same job. There is no doubt the job is faster with the skid steer, but rental, plus deliver/pickup, plus operator may make the costs close for the two alternatives. However if the dirt must also be spread, the skid steer choice easily wins because the cost of delivery and daily rental is already covered and the spread task is accomplished within the day.
I hope this helps with your decision.
KubieTwo