One word can answer your question the 960 setting on your tractor is for the mid pto for a BELLYMOWER
Well my B2920 has the MMM at 2500. Here is what I see.
Al

Al
One word can answer your question the 960 setting on your tractor is for the mid pto for a BELLYMOWER
Your engine rpm were too low so you had no HP. You need to overspeed the thrower a bit to make your engine happy. I always try to use all engine torque when throwing snow. No point in wasting time.Well as I wanted to try the 960 PTO on the blower in light snow. I got my chance the other day.
It would work but it didn't feel right. I was at 1300 RPM and the tractor was still lugging down in sound not on in RPM. It was not heavy snow.
Something just didn't seem right.
You know the feeling when all the gauges look good but something sounds wrong. That was the feeling.
Al
It has been a while since I've been around ag tractors. I thought the 540 rpm and 1000 rpm were different physically. The 540 has 6 spines and the 1000 rpm had like 20 small splines. I recall the size was similar and in college I learned that the same physical sized material could transmit more power by spinning faster, hence the higher hp rigs would have the 1000 rpm.
So is this 3rd one (1000 small?) be a physical 540 hook up, but then allow you to run at 1/2 throttle to achieve the 540 rpm (and if you throttled up would over speed the implement)? (So isn't this the OP's question?)