I am looking at purchasing a Kubota MX5100 tractor. I cannot decide whether to go with 2WD or 4WD. Big cost difference. I have a 40 ac farm and will use the tractor to brush hog, moving round hay bales and front end loader work. My father-in law insists that I will not need 4WD to perform the tasks I need.
Any advice would help
Your FIL is correct. MFWD (=4WD) isn't absolutely required for mowing or toting bales around. It comes in handy for FEL work.
I had a 2005 Kubota B7510HST (21 hp engine, 4WD, hydrostatic tranny) with the LA302 FEL (4-ft wide bucket). It's easy to get proficient with the FEL with a setup like this.
You just have to be aware of potential problems with FELs and 4WD. For example, in 4WD be sure the front wheels can spin when you dig the FEL bucket into a pile of whatever. If the pile is on a concrete slab and the front wheels can't spin when the tractor forward motion stops, you could damage the 4WD drive train.
And don't lug the engine down too far when filling the bucket. You have a lot of hp with the MX and it's possible to reverse the spin on the engine if you really lug it down. Not necessarily fatal to the engine, but not good either (you lose oil pressure quickly when the engine runs backwards). I've never done this, but other folks on TBN apparently have seen this happen.
I traded that 7510 for a much larger Mahindra 5525 (54 hp engine, 2WD, gear tranny) with the ML250 FEL (6-ft wide bucket). It took somewhat longer to get proficient with the FEL, but I do OK now. Truth be told, I miss the HST more than the 4WD.