Andy,

My 'gut' would say go for a heavier bullet and a bit more speed. Personally I would not load a 73 action up to the gills.

By limiting yourself to another 357 in the low wall you might be restricting 'other things'.

If you went for the 38-55 Low Wall you can easily do 100 yards but if you had the opportunity it could be loaded to work very well at longer distances, people use this case for silhouette shooting and that's out to 500m, but the weight of the low wall would make full loads a bit unpleasant so somewhere in between.

If wanting to stay with one cartridge then heavier bullets in both the 73 and Low Wall for the longer range,

BTW you state the MV limit, what is the energy limit out of interest, 2150 is pretty darn quick for a 357

Brgds Terry