I was going to say the NH 575 requires a lot of HP. The tractors you listed are all pretty solid older machines. In the IH the xx66 are, in the opinion of most, the better machines, but a lot older now. My two neighbors use IH 856 and JD 4340 in front of their NH 575. Both do a good job. I thought it was over-kill at first, but then they make 40,000+ bales/year on some pretty hilly terrain. With the combinations listed, there is never any hesitation or lugging and that is important. No risk of the load pushing the tractor either!
I had seriously considered buying 2 tractors, a CUT and an older bigger machine for my operation, but I really needed a UT for some of the clearing projects and to get around in the winter. So, I decided to get something big enough to hay and small enough to be useful and mobile.
There is a 50-50 possibility that I will dramatically increase my haying operation to 25,000+ bales/year for next season. If this occurs, I will just go ahead and buy a larger unit specifically for making haying. It is all up to the NY State and the future of the horse race track across the river from me. If it opens, I will be working hard to get a contract to supply hay. There is plenty of active but under utilized hay land in the immediate area that could be leased for horse hay production. Just a waiting game...