Outhaul settings:

Cat rigged, 20mm upwind in heavy air; a bit more (20-50mm) if lighter wind. Downwind, 100-250mm, depending on apparent wind speed. I sometimes sail cat rigged sans spinnaker, and then I usually have the outhaul very loose downwind, 200-250mm.

Sloop rigged, 10-15mm upwind; 100-150mm downwind (depending on apparent wind).

I have now stopped tightening the outhaul taught to 0mm, even in heavy winds because it ends up pulling the bolt rope out of the bottom of the mast. Leaving the outhaul just a bit off the boom prevents this, and I still flatten the sail fine up high.

FWIT, my sails/mast allow 4.5 Ronstan numbers worth of downhaul.

This past weekend we were sailing in conditions where you had to keep the top half of the sail flat and nearly backwinding to prevent capsize. I had my mast settings more extreme (more prebend and tighter diamonds) than I ever had at:
Spreader rake 50mm
Prebend 48mm
Diamond tension 38 Loos

Previously my prebend was 30mm with looser diamonds (33). I was trying to keep the gusts from deepening the sail more. Although it was hard to pay much attention to the nuances since we were just trying not to wash off the boat in the waves, speed seemed okay because, for comparison, an A-cat (Bimare XJ) could just barely pass me upwind. But had the winds been lighter, this would have been too much prebend.

Here are the setting Ashby suggested for my rig and sail:
Spreader rake 55mm
Prebend 30mm
Loos 39 (ends up 33 for me to attain the other 2 numbers)

I think Goodall suggests:
Spreader rake 40-65mm
Diamond tension 42 Loos

McCook suggests:
Prebend 35-38mm


Here's what I'm trying now (0-10kts/10-15kts/15-20kts):
Spreader rake 45/55/60mm (for your longer arms, 70/80/87)
Prebend 20/30/35-40mm

(I'm mostly sailing uni but try to keep mast the same for sloop)

As you suggested, the diamond tension is to be taken with a grain of salt since Loos gauges seem to differ.