What I was trying to say is that in my qualitative experience, TenD is below average in terms of downproofness, wind proofness and water repellency, so opting for something a little more proven for the shell portion of the bag would be a sage decision. It's not worth compromising these attributes for an ounce, and fabrics like Thru-Hikers M50 boast excellence in all of these attributes for the same weight as TenD.
It's been a while since I used any Pertex Quantum, but my recollection of this fabric is that it worked well as a shell. So given the choice between these two fabrics, I would choose Quantum for the shell. I haven't compared the two head to head. If Zpacks offered more fabric choices then something else would likely top the list for a shell choice. As I recall, there may even be different versions of Pertex Quantum (ie. Pertex Quantum Eco?) so I can't really speak to the characteristics of Quantum with any accuracy.
To me, wind resistance is the least important of these three attributes. If I often cowboy camped it might be more important, but I'm normally sleeping inside an enclosed shelter where breezes are low, so it's a tiny consideration as long as the fabric is reasonably windproof. I haven't determined that Quantum is more wind resistant. TenD seems adequate in this area, whereas my (vague) recollection of Quantum is that it's pretty good. Either way, they're both likely good enough.
Water repellency is more important. Theoretically it shouldn't matter too much to a double wall shelter user like myself, but it's a nice extra line of safety for a down bag (for zero weight vs. M50). Should I ever have an issue with my shelter (ie. fly sticking to inner) or on the trail (ie. waterproof stuff sack leaks) or in the tent (spill water on it), then hopefully the water repellency would mitigate any trouble.
Downproofness may be personal preference. Perhaps I'm just anal, but I'm not particularly fond of having a constant exodus of down from my quilt, even if the total amount is fairly insignificant. With TenD, there is ALWAYS several tuffs of down on their way out of my quilt. Often it's not large feathers either, it's down clusters with maybe a super tiny stem. My previous quilt was made of M55 (supposedly the same as the current M50 (2nd generation)) and I never saw a single down clump or feather come from that. Both quilts were "900 fp".
So to wrap this up, to have a nice soft feel TenD compromises downproofness, likely compromises water repellency and might compromise windproofness. For the inside (lining) of a bag this might be a compromise worth making, but for the outside it doesn't make sense trading these attributes for feel, since you aren't even touching this area. Unfortunately the other option (Pertex Quantum) is heavier. A fabric like M50 would be ideal for the shell. It's the same weight and won't let a smidge of down, wind or water get through.
I'm at about 100 nights with this quilt.