Well, I'll tell you about my Power Trac experience... you don't have to read it, but I'll tell you anyway... :laughing:
I have a 2001 PT425. Its got a 25HP Kohler horizontal shaft gas engine. Meant to be run at 3600rpm. There's several variations over the years, but basically, there's a variable volume tram pump for moving the machine. There's an 8gpm @ 2500psi pump for the main hydraulic PTO (powers any implements like mowers, brush cutters, tillers, trenchers, etc...). Then there's a third pump that puts out I think about 4GPM@2500psi. That powers the steering, front end loader and what's called the AUX PTO. The AUX PTO is what operates the quick attach, and any implement with power direction control, like the left/right movement of a snowplow or broom.
There's 4 wheel motors hooked up in some sort of series parallel arrangement. This allows for turning the tractor without skidding the wheels. Its also basically all wheel drive all the time.
The variable volume pump provides power to the wheel motors. There's no "transmission" to speak of. So, there's only one speed range. There's no hi-lo for gearing. Its 8mph forward and 8mph backward. So its a compromise between speed and power.
So, to address the speed VS power issue:
I don't need power to the ground for the tasks I do. I don't pull stumps or pull a dirt plow, so traction isn't an issue. I don't "road" the machine, so I don't need high speed. At 8mph forward and reverse, its a heck of a good material mover. And its a heck of a good snow plowing machine. I usually travel around 4-5mph when mowing, so its good at that as well. Brush cutting, fork lift, loader, tiller, post-holing, etc... it just doesn't need low-end grunt.
And, my machine is only 1500# anyway. If I needed to do more, I could buy a bigger model, as they make several.
So, your 0-7 may be about the sweet spot for most tasks, but I'll guess you'll be lacking a bit of low end grunt if its hydrostatically driven. Be sure to test that part out thoroughly.
Good luck with your project.