Look at it this way....
PT422 - $8500 = $386/HP
PT425 - $11,500 = $460/HP
Back in 2001 when I bought my PT425 the price per HP was almost equal between the two models and I got a free ROPS.
The only differrences between the two units back then was HP, engine manufacturer, included ROPS and canopy, and dual steering cylinders.
Today, the differences are HP, dual steering cylinders, ROPS and canopy, higher torque wheel motors and an 8" higher lift capacity.
Is that worth $3000 more? Let's say you deem the ROPS mandatory, so that brings the price difference down to $2500.
Wheel motor torque:
I can tell you that my 2001 PT425 has the same wheel motors as the current PT422 and there are times when I could use more torque going up and down the hills in the forrest on our rural property, or powering over logs on the forest floor. That would be a big plus.
Dual steering cylinders:
As mentioned, several folks have found single cylinder steering on the 422 to be a design flaw, as it has torn out. Plus you have the added false floor to deal with, not on the 425.
Higher lift capacity:
My 2001 PT425 has the same lift height as the current 422. There have been a few times I could have used it. 8" is a lot when you're talking about 4'4" VS 5'.
So, I would say, if you can afford it, spring for the extras in the 425.