I am going to be purchasing the HH Explorer Ultralite A-Sym.. and I definitely wanted to get the larger 12'x10' polyester hex rainfly, as it is a free upgrade.

However I was also looking at the 12'x11' silnylon hex rainfly. It costs twice as much.. is there any other differences besides being lighter and a foot longer?
Is silnylon more durable/waterproof/whatever than PU coated polyester.. or is it just lighter?

Anyone have any experiences with either the larger polyester hex fly or the silnylon one?