Phat
As I posted at another forum and managed to offend another manufacturer with my opinion, I would not switch from the TT silnylon to the LW Cuben used by some.
(I would consider a more opaque and heavier duty type...)
Many have speculated on waterhead tests and all of that about silnylon but Richard Nisley tested the LW Cuben to be less waterproof particularly when "aged".
See his results for yourself :
https://skydrive.live.com/?cid=99d830397376f22d&sc=documents&id=99D830397376F22D%21287

BTW , I don't think those figures really apply directly to tent material because the Suter test puts an even pressure across all of the fabric tested . Rain does not fall like that neither you have a 1 m column on top of the tent, but it is a comparison.
Franco