I think he means world records, not per weight class. Seems to be something with overall potential, as far as what has been recorded anyway.
With that said, unless you are trying to break a world record, do what makes you strong. In general, conventional is harder on the back, and sumo is harder on the hips. If you have no limitations with either, pull both.
Squatting sumo will build up the hips, a lot, but pulling sumo seems to help drive the knees out harder. If your adductors arent awesome, pull sumo, it can only help IMO.
The stimulus is different anyway, and you have different ways to hit the hips (just like using specialty bars to squat for different emphasis on the back). Pull sumo, semi-sumo, 1" or 2" deficit in each of those different stances (full sumo with the biggest deficit you can reach is crazy on the rotators of the hips).
It's just another training tool.