I also have a bervac 64 blower mounted on a MT180D.(20HP)
To answer your question I have ONLY run it on my 2 PTO setting.
Flat out in 1st it kinda flops the snow out and barely over the snow banks so I always use 2nd, generally @ about 2250 RPM and get very acceptable performance .
In low, even at higher RPM I find it kinda useless but do use when in hard chunky icy stuff otherwise I shear too many bolts.
Have done that for 2 years without adverse effects.
I use grade 5 bolts for shears with nylon lock nuts and blow them from time to time on chunks of ice.
The 5's cut clean rather than get mangled as the softer ones do.
Keep your augers well greased if you want to be protected.
I found out the hard way as I destroyed a 'used' 4ft bervac because the previous owner did not bother to grease it.
Keep the turbine shear bolt snug otherwise it will distort the 'ears' before they shear.
Like your Yanmar, my MT is a bit confusing as I also have 3 PTO speeds
My manual says 1st=540@2660RPM and 3rd=1000RPM=1793 for 3RD . (with no mention of 2nd)
On the other hand it gives: 1ST=623RPM@2700, 2ND=919RPM@2700, 3RD=1505RPM@2700,
I gather that the other speeds are related to some Asian standards, perhaps rice paddy equipment.
Judging by the performance @22-2300RPM in second I feel that it is correct match.
Shame that Bervac only made the turbine with 3 blades.
I plan to modify the blade from the 48" into 4 blades as I believe that it will greatly enhance the operation.
Hope this helps.