It's not the HP that really matters with the big BP's. It's the fan, fan housing, and tube design that makes the difference. All the big BP's have enough power to turn the fan these days. The 8001 was a big dog in its day, but if you try a new 8500 next to one you'll see a noticeable difference in performance. The 7500 will also outperform the 8050 and 8001 by an appreciable amount.
The early 8500's had issues with overheating (that were covered under warranty quite nicely), but that has siince been worked out and I have yet to hear from, or talk to, anyone whose had anymore issues with them.
The 7500/570 will blow just as large a pile of leaves as the 8500/580, but they scour much better when the leaves are wet or other debris is stuck down to the ground. They are lighter and use less gas too. Don't overlook them just based on specs. Do what I did, and run them in the real world on fall leaves and you'll see what I am saying. You won't be missing anything by going to the 7500/570. All four of these machines are definitely ahead of everything else right now.
One other thing, the Husky versions have far superior shoulder harness systems to the RM versions, and any other blower for that matter.