Re: Taln's possible blade(s). Earlier people were remarking on how ornate Honorblades (including Szeth's) are, but the quote in the prologue doesn't really say that.
We know they are "works of art" and have a "flowing design" but that does not imply "ornate." A Katana from Feudal Japan is likely a work of art, but not necessarily ornate. A Ghurka can be considered to have a flowing design, but also does not imply ostentation. I would agree they are likely stylized (the inscriptions imply as much) but I don't think they would be as elaborate as I inferred from the descriptions earlier in the thread.
Do we know for sure that the second blade Dalinar bonded really came from the Madman known as Taln? We know that's what he told Amaram:
But it seems just as likely that it was one of the Dual-won Blades that was used for the ruse. Especially if the Madman's blade had had no gem and Dalinar did not want that revealed.
Civilian Airliners typically fly FL350+ (35,000 ft Mean Sea Level) when transiting more than 2 hours. Small Passenger Aircraft (like B350 King Air have a service ceiling below 30,000 ft, and more commonly fly around 20,000 ft MSL. They are generally undetectable by the unaided eye at those flight levels. With moderate humidity (causes haze at altitude) and or cloud cover, they are generally not visible at 12,000 ft. UAVs, which range from about 2 ft to almost 30 ft in length, are generally undetectable by the unaided eye at 6-10,000 ft. Especially without auditory cues.
Air pressure is such that unpressurized aircraft do not require supplemental oxygen for passengers at 10000 ft (when over 10k ft, supplemental oxygen is required and the time of useful consciousness decreases exponentially with each 1000 ft of altitude).
In the final battle, we know Szeth and Kaladin got above the cloud tops, which for a normal thunderstorm (and this was a Highstorm) can be anywhere from 15-35,0000 ft MSL; but I would say it is often 22-24,000 ft.
Terminal Velocity of a skydiver in freefall is about 195kph (120 mph) when splayed with wind resistance, and can reach over 320kph (200 mph) when arrowed forward, limbs tucked to reduce air velocity. So, with a single lashing and assuming Rosharan gravity is about equal to earth's, the average Windrunner trying to fall quickly over distance would be about the speed of a C-130 Hercules over distance.
All that said, even a few hundred feet would seem high to somebody new to this, so Kaladin's estimate of how high he thought he was when first experimenting over the shattered plane is not reliable. We know he can go higher, but I doubt he was over 5000 ft since the terrain he describes would have lost significant detail at higher altitudes. Roads can blend in and be difficult to see that high; and the chasms aren't a contrasting color, especially at night with only moonlight.
All that said, I think both theories for Nalan are equally viable, including the third possibility that we don;t know enough about the Heralds and they could have an innate ability to travel through Shadesmar without the Surgebinding of Transportation, like other known Worldhoppers.