My experience is that high quality glass is more important than high magnification. I guess you already discovered that with your older Leupold spotter.
As you go to higher mag, you become limited by other things like stability (need a bitter tripod), Brightness (need a bigger heavy objective lens so that image does not become dark) and heat waves in the air if you are hunting in hot weather.
I took my 20-60x65 spotter on a pronghorn hunt, with a big heavy tripod. It was rock solid, but it was also super hot and sunny and due to the thermals, most of the time I was just as well off with my 10x binos.
Also, since binos have two eye cups, they make contact at two points on my face, which helps stabilize them.
I have found that the low dispersion glass advertised in some brands really does make a difference.
I did a little experiment by setting up a tripod and looking at the detail of a distant object.
I compared two 20-60 spotters (Vortex Viper and Bushnell Elite) and a 11x Maven bino (which are heavy and kept in the car), and some 10x Tract binos (these are my primary field binos).
Those all have low dispersion glass and of good design. Though the spotting scopes produced bigger images, I could see just as much detail with the lower power binos.
When I then tried some poorer quality binons/spotter the detail was lost.
Heat waves/mirage happen from the sun heating the ground. Air that touches the ground heats up and then rises. The hot rising air is of a lower density than the ambient air and so creates a distortion. This effect is greatest just above the ground, and so looking over long flat distances on a hot sunny day creates a lot of distortion and renders most scopes useless.
If on the other hand you are looking across a valley then most of the distortion is well below the line of sight and the effect is much lower. Overcast also helps, since the soil surface is not being heated as much.
All the pronghorn hunters out there likely have a lot of input on this topic.
So, at least with my limited experience, I would only use a spotter if I was looking long distances over cool air and preferably across valleys instead of over flat terrain.
At least until some innovative company creates an adaptive optic spotting scope to correct for heat waves (just like astronomical telescopes do to correct for atmospheric distortions).
