The heaviest trains to run were 1,000 ton cement trains between Northwall and Cork, they were hauled by either a 071 or 201. They were specials, the max limits are currently 36TEU with 740 tons. There was talk last year of going to 40TEU on the IWT liners but there is at least passing loop that can only take a 201 and a 36TEU 18 47ft flats maximum and thats were IWTs regularly pass each other. That loop would no longer be an option.
Great to see if they do increase the limits to make freight more economic assuming they can fill a 40+TEU train every time. Axle loading is another issue, with a loaded tanktainer, only one can be placed on a flat wagon because the axle load limited would be exceeded with two. That's why you see only single tanktainers loaded leaving Dublin but the return empty have them doubled up.
As it is an autoballaster loaded to it's max will exceed the Irish axle load limit, they are never fully filled and have a load gauge on the side of each wagon to make sure they stay in the limit.