New Silk

I think I have found a new silk for my ball gown.

It's a taffeta and more expensive than what I had picked out originally. But for only 4 yards I can swing it. I'm really torn though, not sure the ball will make. Do I get it now and just spend the money or do I wait with the possibility it will take forever to get here and either I will have to rush the construction or the fabric won't come in time? This is something to think about after Christmas...