I looked at this and you're quite right. In a fresh breeze, under all fore-and-aft sails, I can do 3 and a bit knots four points from the wind, which seems way too good. I will see if I can make some time to mess with it over the holiday. I can try some combination of making the fore-and-aft sails less efficient (essentially making them smaller) and increasing the drag on the masts and rigging.
It was a long time ago, but I believe most of the tweaks to aerodynamics are things that are exposed. In the physics menu on the left, wind lift coeff. and drag coeff. should have straight linear effects on the lift and drag forces. Lift is zero at angle 0 (the wind is parallel to the yard), reaches a maximum at some angle (currently 30 degrees), and falls to 0 when it is perpendicular to the yard. I think it's modelled just as a sin curve, except you can use the max lift angle slider to shift where the peak is. Lastly "griping" on the right isn't aerodynamics, but controls how far forward the lift force on the hull acts. If you put it higher, the ship gets less stable around the yaw axis, meaning that tacking is easier, but on the other hand balancing the sails is more important; and vice versa.
Edit - I'm pretty sure the aerodynamic sliders don't do anything to the drag on the masts etc.