All other discussion about the merits of this and that way of measuring things can be put into perspective very simply.
If you can get one of those bales on a truck, take it to the dealer and have him show you that his machine can unload it from your truck/trailer and carry it around the lot.
The talk about where capacities are measured is an interesting intellectual exercise, but even the magical 500 mm (19 inch) distance will not do you any good with round bales since the weight is not centered there. The bales, if speared at the end, will project out from the pivot point about 4 feet, maybe a bit more. Not all bales are equal, depending on what they're made of.
Finally, are these loader ratings at the pin made with bucket on or off? Buckets are not light. How high do you need to lift the bales? Weight to maximum height is not the same as basic lifting.
Bottom line -- get more loader than the numbers say you need and really push for the dealer to show you that it will do what you want done without strain.