I'm gonna translate that as "wild azz guess". Not being disrespectful, I know your basic approach was logical but it really wasn't data or experience driven. PTO requirements listed by manufacturers are typically simply a regurgitation of the gearbox limits. There is absolutely no question for example that the NX4510 can run the BB720 efficiently. Box blade capacity is more limited by traction than horsepower and I can spin my wheels pretty easily in dry or wet conditions. Snow plow as in plow is likely to be another traction issue. Snow plow as in blower is indeed a HP issue but a six foot blower is certainly fine for 40hp. Unless you want wider than 12ft that is still just one up and back run. Travel speed I haven't checked and I know that the 6010 has bigger rears so maybe has a couple mph on the smaller version. On a highway that might make a bit of difference. I cannot ever travel at close to top speed on my DK on pasture or farm roads. Way too bumpy.
I know you are planning to do foundation work. Wouldn't either a BH attachment or simply renting a mini excavator make more sense than trying to dig out a foundation with a box blade and loader??? The money saved on the 15hp and ultra box blade would take you pretty close to a nice backhoe. Or, you could rent a mini excavator for a week and have beer money for life.