What is more aero? A single bottle on the down tube or a rear mounted set up with nothing on the frame? Hydrotail specifically and aerotubed bike.
Varies. Do you have big thighs and / or pedal with your legs pretty closed? Do you sit rather backward on your saddle? A hydrotail might be more aero…
I thought the seat tube was a better option than downtube if you have both and only need one bottle (for races)? Have you guys ever compared the two?
When in doubt, check the main page.
http://www.slowtwitch.com/mainheadings/techctr/waterbottles.html
Different bike, different rider, you get different results. John Cobb’s test is hardly the final statement on hydration aerodynamics on bikes.
Different bike, different rider, you get different results. John Cobb’s test is hardly the final statement on hydration aerodynamics on bikes.
In some of my testing I’ve found it sometimes even appears to change depending on what front wheel is used as well…and, of course, the wind angle 
Someone once said that “This positioning thing is HIGHLY individual.” Well, that goes for a lot of aero gear as well…(helmets and bottle placement/type especially)
Should the lettering on the water bottle be facing the front or rear, and does the flavor of Gatorade make a difference?
Hello… scrape the lettering off… makes the bottle lighter.
Should the lettering on the water bottle be facing the front or rear, and does the flavor of Gatorade make a difference?
Yes.
I fully expect to see you on Sunday with water bottles that have been sanded down to bare plastic! 
Are you heading home right after the race?
Different bike, different rider, you get different results. John Cobb’s test is hardly the final statement on hydration aerodynamics on bikes.
This is in fact correct. same set-up, different rider - different results. Same rider, different bike - differeny set-up results…
ONE set up does NOT fit all