I'm no expert but I'm thinking you will get better long term durability from a good garden tractor. Perhaps something like a
Ingersoll or a mid to late 90's Simplicity Sovereign. The only issue is the more rugged machines tend to cost more. It has been a long time since I priced a ingersoll but there are not cheap. I hope others here will offer suggestions. The JD 400 is supposed to be a good machine as well.
Another option is to find a nice used Kubota BX. Perhaps one of the little 18hp models like the 1860 or the earlier versions like the
BX1500. But your budget is going up quite a bit compared to the $3k you had been planning on spending. I think Kubota still is offering 0% for 60months? But now I have you into a much heavier, larger, more expensive machine then a JD x300 lawn tractor. There is no question a little 18hp BX is a great value, its just a lot of money for someone who was looking to spend $2-3K for a mower.
Perhaps someone else can speak up and provide some info on the JD x500 series, if the tranny is decent.
With a $3k budget I think you are either going to have to go 10+ years old used or you are going to have to up the budget. Or get a cheep lawn mower and hope for the best. If it dies you are only?? out a few $k.
I don't know if a ZTR can pull a cart? I thought they generally are strictly mowers. Might not meet your needs.
Do you have a set budget?