I prefer using negative outhaul on all points of sail.
For one i can't be bothered with the hassle and added weight of adjustable outhaul.
Also,i like to use a smaller sail than is necessary for comfort more than performance. I dislike the feel of 7m or larger size sails,they ALL feel heavy to me.
Using a smaller sail,i use the high clew eyelet,use max negative outhaul and a bit less downhaul,all helps to power up the sail,though nothing will make up for that extra half a metre of sail for pure performance.
Reckon it's a bit of a myth that bagging the sail out is not good for upwind. If the wind is the consistent,yes a bit of positive can help. On the river, conditions are so on/off that you need the power in the lulls to get upwind.
Adding extra downhaul than is needed results in too much spilling of the wind,killing upwind performance hugely.
yep,
as with nearly every other sail on the market. 
not enough outhaul makes the sail back hand heavy which translates down through the legs into the fin. crabbing persists etc.
not enough downhaul makes a sail feel heavy.
this is one of the reasons people use adjustable outhauls. bag it out off the wind, tighten it up upwind.
to fat a sail entry is very poor for upwind sailing. a windsurfer is a planing vessel not a yatch.
My 6.3m warp feels half the weight of my 7m warp,another reason not to use the 7m.
The 7.1m KA i had felt bigger again.
May only be a few hundred grammes difference but i repeat it feels twice as heavy,and/or bigger!
Only ever sailed with negative outhaul really,short of a strong winter front. Most agree that positive outhaul does help upwind, though for me especially thru the lulls negative works best on all points of sail!
Agree,positive outhaul does help cam rotation in a big way.
I bet this guy knows what he's doing!
If you still don't get it after watching this vid...
There's a second one with tuning tips, let me know if you need that one
