There is no reason why they can't do 400ktpa but with grades of...

There is no reason why they can't do 400ktpa but with grades of 8kg/m3 they will need ponds significantly larger than what RWD will require.
What SO4 saves on roads they will spend on ponds.
But at the end of the day raising 8M is a good result for any junior and don't forget the 40 cents would have been pumped up for the raise.