RE: best allround wavesail on the market?
I would say a mid weight 5.5 sail is around 4kg. 3.5 would be very light. A superfreak is 3.55 in 5.5 size, I believe. Its probably hard go go signaficantly lighter and both stay strong enough and keep attention to detail.
As for SOs. The 5.3 is recemmended on a 430 (438 luff) but at 75 kilos will work great on a 400 too. The 4.2 is rec on a 370 and is 394 luff. It can definitely be used on a 400, but will work better on a 370. So, I would say you can rig 4.2-5.3 on a 4m mast "without too much lack of performance). The same goes for Smack 4.3-5,3 (and here the 5.3 is rec on a 4m mast (424 luff). Again, the SO is a wonderful sail, but have a look at the Smack too. They are not at all what they used to be, and I would say they are an even better all round wwave sail for most peoepl than the SO (but it IS a matter of taste).