I too am looking into a possible used MX ... As I want pre-computer, no emissions ... Unfortunately that far back the biggest engine is "marginal" in the MX 5100, with PTO HP of only 44 in the gear model ... I have set a preference of a minimum of 45 PTO HP for this next tractor, to add to my little SCUT TLB ...
An M5700 61HP engine, 52 PTO HP, or The M6040 63 engine HP, 56 PTO HP ... Is quite a bit larger, but the older M5700 leave me with more weight leeway on my trailer ... The M6040, and it's big brother M7040 in 2 wheel drive ROPS can fit, but are much closer to my 5,000 Lb carrying capacity ...
Gear, 2wd, no loader, and ROPS is fine with me ... PTO HP, and under 5K weight is most important to me ...
I'm tentatively looking now, but not ready to actually buy until my house is paid off this spring and debt free again ... Looking for less that 2K hours ... As I'm seeing some on line adds for 4-5K hours, seems like I'd still get quite a bit of useful life out of it, as long as it has been maintained.