Trex:
At max flow you should get a bit over 600 rpm from the motor, which (for me) is close enough to the standard pto 540 rpm for three point hitch mounted mowers.
Will you have enough power at the mower? If your system has about 2500 psi, which is close to the intermittent maximum for that motor, after system losses and motor inefficiency losses, you will have about 10 hp to the gearbox shaft.
I did something similar with an 11.5gpm flow and 48" mower. Even light brush slows it down enough that you have to creep along very slowly. Mine is certainly an improvement over a weed eater with a brush blade, and it serves my purpose well enough, but there is not enough power to just drive through brush like you could do if the mower were on the three point hitch and PTO powered.
My mower is a Bush Hog Squealer and has a 1:1.93 ratio gear box. I think the higher ratio is used to give an adequate blade tip speed on the relativly short 24" cutting radius.
