Here's what I use, just as a data point that's not worth much:
In cold water:
Hollis 38 lbs wing
Al backplate
~6 lbs p-weight I cast to fit the backplate
STA (required because of how the p-weight mounts)
Adjustable harness with Hollis ditchable weight pockets
trim pockets on both cambands
In warm water:
Same wing
same backplate
single piece harness
trim pockets on both cambands
In cold water:
Hollis 38 lbs wing
Al backplate
~6 lbs p-weight I cast to fit the backplate
STA (required because of how the p-weight mounts)
Adjustable harness with Hollis ditchable weight pockets
trim pockets on both cambands
In warm water:
Same wing
same backplate
single piece harness
trim pockets on both cambands