I have a JD 757 60", bought it in 2005 from the dealership, it had been a demo so I got what I think was a good price. I have heard, from my JD mechanic, that you need to be really good (I neglected this for the first couple of years and only remember to check that my husband and son did it about once a month) about cleaning the grass out of the motor area, and keep the maintenance up because they will "blow up", in fact, he says mine and one other are the only two that he hasn't replaced some major engine part.
That said, last year I had to replace some 'clutch' mechanism, I'll be honest, I am not a grease monkey, I operate the equipment and trust that my mechanic is honest, so I just cringe when it is an expensive repair, and that one was somewhere near the $500 mark. After that, a plug came unplugged, the one that seems to connect the power to the mower deck when you turn that on, twice, but once I realized that it wasn't getting completely plugged in, it has not come loose again. Also, we mow around 2 acres of lawn around the house, barn and what I call the common areas and edge about a mile of fence in the horse pastures with this, 2 laps, before mowing with the tractor. I also use it for my smallest horse paddocks (super small for quarantine, dieting, or injury induced rest limited movement of horse).
It is fast, and if my horse pastures were lawn smooth (they are not) it would be awesome, but it beats the operator to go at the fun speed in a pasture.
I'll have to go look at how many hours are on that mower, but it gets heavy use, even abuse sometimes.
I will say, I should probably consider trading it in on a narrower model. When we bought it, we had a lot more open space, now my husband has put in a bajillion (ok, probably only 125 or so) trees and shrubs and several gardens in the lawn/yard area making him do a ton of push mowing.