in marginal conditions I let out the outhaul up to 3-4 cm and release the downhaul 1 - 2 cm. Now I hear an interview by a bigname sailor who says once the downhaul is set leave it and only adjust the outhaul. I feel as if the downhaul change makes a difference but is it in my mind or what? This is for onshore b&j.

I think that the added 'power' from letting the downhaul off is often an illusion.

Decreasing the twist puts the centre of effort higher in the sail, which in turn means that it takes more effort at the boom to counter the pull. Which would be fine, except that the sail's pull is now more sideways and less forward. So the sail is now pulling harder, but in the wrong direction..

I had a sail that wouldn't twist properly regardless of how I rigged it, and the difference between that sail, and one from another brand that twists nicely was major. The nasty one left me tired and frustrated without having actually really got planing. The nice one was planing with power to spare and required much less wrestling. If I let off most of the downhaul and remove the twist from the nice one it behaves much like the nasty one - tonnes of pull, but not much go.

yer the downhaul makes the sail stable and stops the power moving all over the place.