Good choice on the Shangri-La 3. I own the Hex 3 and love it. A few comments that I have not seen addressed elsewhere:
1) There have been several comments about not using the Hex 3 in summer. What many people don't realize is that you can open up both sides of the door panel, so that 2 of the 6 side panels are rolled back. This effectively opens up 1/3 of the shelter for nice breezes. The peak still overhangs enough that if you sleep perpendicular to the door and push the pole over, you can both still be completely covered by the Hex (think oversized Gatewood cape for 2). Plus, if you use long tent stakes, you can get a good 8 inches of space between the ground and the Hex. So the Hex can indeed be a great warm-weather shelter as well. Hunkering down simply means closing the two door panels. The Hex 3 only has a pullback tie for one of the panels, but if you roll up the other panel, you can secure it by staking out the guyout.
2) If you both carry trekking poles, sew loops into the ends of a 5' grosgrain strap. Connect both sets of poles as you normally would, so you have two very long poles. Then, place them as an inverted V, using the grosgrain strap to prevent them from sliding apart. This will allow you to sleep in the middle of the shelter, with 5' of sleeping width. It eliminates the center-pole claustrophobia, and gives you much more headroom, since it effectively opens up the space in the top center normally occupied by the center pole.
3) I've adapted a setup technique I learned from these forums. The great thing about the Hex 3 is that the side panels are the same length as the radius (when measured from the panel corners), which is 5' exactly. This means the Hex floorspace is made up of 6 equilateral triangles, with all sides 5'.
If you have 5' poles (my Komperdell CFs' are exactly 5'), you can 'triangulate' a perfect pitch. Start by placing a stake in the center. Use one pole as your radius and the second pole as your perimeter side. Work your way around the perimeter, with one pole touching the center stake and the other pole touching the last perimeter stake you placed. Where the two poles meet is where you place the next stake. I've done this 4 times now and have gotten a perfect pitch every time.
In the 2 years I've owned the Hex 3, this is the first time I've accomplished a perfect, taut pitch, without over-stretching here and there. It also means you can precisely determine where you will be lying down. Just place the center stake in the middle of there you want to by lying down, and put the first perimeter stake where you want the door to be.
I only wish that someone made a lightweight, rectangular 2-person inner bug nest that comes to a point in the middle apex. This would save substantial weight over the Hex 3 nest. I'm thinking something like an Integral Designs Silshelter bug liner, but with the peak over the center rather than over the head end.
4) And finally, I find it interesting that most people never think of using a bivy in a Tarptent. Most seem to think of using a tarp and bivy, tarptent, OR double wall tent.
If, on the other hand, you used a tarptent AND two lightweight dwr or wp/b bivies or overbags (Montbell Breee Dry-Tec comes to mind), you'd still be lighter than true double wall tents (and lighter than the Hex 3 with stock inner nest), and be much more versatile. There are many advantages:
a) You'd have the sewn-in bug-proofness, breathability, and ease of setup of the tarptent.
b) You'd have the wind and condensation resistance of the bivy (creating a quasi-double wall tent), and still be protected in the event of tent failure.
c) You could just use the bivies for starry alpine nights, or just the tarptent for warm buggy nights.
d) You'd have more room than a double-wall tent.
e) If you get a tarptent that only uses trekking poles, you are further protected from poles snapping in a double wall tent.
f) wp/b overbags would double as emergency shelters as well as act as stuffsacks for the sleeping bags.