I believe the BX series Kubota would be small step up from the JD X540. BX has MFWD, 3PH, rear and mid PTO as standard equipment. I am not sure how the "GR" series Kubota would compare to the x540 though.
My son has a X485 with 1300 hrs and loves it but it is smaller than my BX1850 & weighs around 400 lbs less. The X series deere turn sharper than the BX kubota.
Both do great job at mowing the lawn.

