Not sure there is a definitive answer to the first question - obviously it depends on the plant, growing conditions, etc. Plumerias (and many other succulents) can be rooted from very large cuttings because (by definition) they store plenty of water in their stems and don't depend as much on the roots they don't have when they're getting started. My experience has been that large hardwood cuttings of deciduous plants may root, depending on the species, so that procedure may work for grapes, or it may not. I've had very large branches of Crape Myrtle and Willow root "by accident" when used as stakes or edging over the winter. A softwood cutting (taken while the vine's in full growth) probably wouldn't make it at that size, since it wouldn't have the ability to supply all of that green tissue with moisture. As to potential production, I can't say, but I'm guessing that all grapes would be propagated that way if it were the most efficient method. Most of the fun of gardening is experimentation, so why not give it a shot if you have the space, time, and cutting stock?