One important point to keep in mind is that weight can not be considered by itself. You have to consider the power to weight ratio. Look at two of the fastest sailing craft in the world- Yellow Pages and the windsurfers. One weighs about 350lb and the other weights about 30. Both have achieved virtually the same speed while the first being about 10 times heavier than second. It's all about power-to-weight.
This is why having a heavy boat is generally not beneficial, because the added weight contributes mostly to drag and little to righting moment (which equals power). However having a heavier crew (movable weight) contributes to more power generated from the rig (as long as the wind is strong enough to support the fully hiked crew).
