I think we've all have had durable boards that were fast. Top speed isnt that affected by board weight, probably acceleration is the most affected thing.
Crashes during a crowded race are very usual, as well as the usual dings when carrying the board. I think that for all but those lucky brand sponsored sailors, a more durable board makes sense. We are not talking about changing the board, just offering a cheaper version. I've heard lots of people comment this at the Longboard Forum...check this:
Anyway this is just an opinion folks. Have fun.