I have a 64" rear blower (SB1164). Every Deere sales person I talked to suggested that it was to big for my 2032R. One begrudgingly finally sold me one. I haven't had any issues with it. It if fills up I slow down. But I also have 6hp more than you have at the rear PTO.
Deere won't recommend anything larger than the SB1154 for the 2025R.
Hold on, I texted the dealer with my concern and he texted back and said that he messed up and that I in fact was getting 60" farmking made be Buhler, now I wish it would hurry up, it's the only thing that I'm waiting for.
You'll be fine. And you would have been fine with a 66", provided that your tractor could lift it, though you may not have liked the performance.
If you "didn't have enough HP" to run the blower, that would mean you'd just have to go slower. If you get to the point where you are going too slow, then you really don't have enough power. Obviously if you have a massive blower, you may not have the HP to get it to work the way it's supposed at all, but then your tractor wouldn't be able to lift it with the three point (or front quick hitch). Basically, when it comes to snowblowers, if you can lift it, you can use it.