I too have had trouble with upwind boat speed; sailing 7 rig, sail 18 months old, recently checked over for stretch & wear, still OK.
Noticed in light wind at Nationals, and last Sunday at Sailing club, Grafham, in F3-4, gusting 5 with shifts on gusts; other times & conditions as well.
At Grafham in morning races I sail against D0, & a Solo. Afternoon all single handed mono-hulls start together: D0, Laser full & Radial rigs, Europe.
Morning races I can usually hold off the Solo, but we get finished after 2 laps of a 45 min race whereas the D0 get 3 laps in.
Afternoon races, again 45 min race time, I am usually up/down with the trailing Laser full rig and Radial.
The Great Lakes Handicap numbers GWSC use (Aug 2016) are:
RS Aero 9 1028
D0 1033
RS Aero 7 1066
D0 blue 1061
Laser Replica 1084
Laser full rig 1115
Laser Radial 1145
Solo 1150
I do keep the boat flat, but I just don't seem able to sail the boat to its handicap.
My suspicion is the sail is not developing as much forward drive as it possibly could, though luff & leech tell tales all good. My kicker may need some adjustment, tail blocks are pulley 2 pulley with boom still horizontal, and top batten tension could possibly be increased, but by how much? Have struggled to find the optimum setting.
Sail depth on foot set to my hand length, approx 7 inches, 18 cm.
Downhaul set for tack strap horizontal no gap under mast button.
Toe strap set for straight leg hiking, though I generally sail with bum on outer deck.
Find the boat points OK but speed relative other boats, particularly upwind, seems an issue.
Though I don't think sail setting is the only issue, but I'm not sure what else to focus on. Help & guidance would be appreciated.