I ordered an LX knowing full well that I really wanted an MX - but the 4310 isn't rated for it. Well, My dealer said I was stooopid and ordered an MX for me. My 4310 is just on the edge with the MX, but we do fine with it.
A 4320 would be perfect pulling an MX. (maybe the salesman have been burned selling them, because they are so spendy...)
I know there are many happy LX owners. But I rarely advise buying it. The sidewalls are too thin in my estimation. Swing wide once and smack a fence post and they will likely crumple. Taping 5 $100 bills onto one won't make it an MX which also has a far superior gearbox, stump jumper, top, and frame.
I feel that the Deere cutters perform better than most. The cutting chamber is engineered for fast clean cutting. Some brands will have real engineering, but not many to the level of Deere's.
As DDivina points out, the standard features can be deleted by the dealer. So one or both sets of chains might not be in the price. In the LX the slipclutch can also be deleted. Don't assume they do this stuff to be 'crooked' there are several reasons why they can come this way. Price is just to most common.