M_Boats: Another Sail Question?

I am narrowing it down to a few lofts to order new main and 128 gen. for my M15. Quotes range from a low of $550 to $841. Also, the sailcloth quoted ranges from a low of 4oz to 6.3oz respectively. I have read no real negatives on any of my possible lofts. I am a recreational sailor (day) and may try a few little races with the WWP guys around here. Winds here are Great Lake style (Huron). How critical is sail weight and what does the heavier cloth add to the sail (durability, longer life, just cost, etc?). *Jeff+* Molōn labe!