Re: Anyone ever use the 2nd PTO speed on their B75
Well, you definitely want to spin your rear mower at 540 RPM (unless you've got one designed for a higher speed, which is unusual for compacts in the US). However, if you are doing light mowing that doesn't load down your engine (or if you have an engine much bigger than what is needed to run your mower), you can save some fuel by putting your PTO in the higher range, and running your engine RPMs down lower to make the PTO speed still come out to 540.
If the 2nd speed of 960 you gave is correct, you'd run your RPMs at 56% of the normal PTO RPM to make the output equal 540 RPM. This trick works a bit better on those tractors which have a 540/750 two speed PTO. Running on the 750 PTO setting only requires throttling back to 72% of Normal PTO speed, so you still have more HP available.
There are other applications where you can use this trick: one that comes to mind is if you have a hydraulic PTO pump running a log splitter or something similar which does not require the full HP of your tractor to operate.
John Mc