A single 300 is more than enough for the dirt, not enough for me with gear and 2-up use.
A single 320 is nice when loaded up with gear on pavement or 2-up.
Dual 320 should be plenty for the street rider ADV user with gear and 2-up. Way overkill IMO on the dirt.
All depends on the needs of the rider.
If I'm going to make left side single mounts, it's and easy image flip to have the right. ;)