I've always been mystified when people talk about silnylon sagging. My limited experience has been with the Ray-Way style tarp, which sags much less in the rain than PU-coated tents I've had.

In the CPAI84 specification, it mentions that in 1995 a group of tent manufacturers submitted a proposal to exempt lightweight backpacking and mountaineering tents, so maybe there's an exception in there somewhere.
_________________________
Always remember that you are absolutely unique, just like everybody else. -Margaret Mead