I wanted to get some votes on this. In both instances I'd be using Ultra Primes. For the Alexa I'd be shooting 444 ProRes at 2K and of course, with the Dragon I could shoot 5K (aspect ratio is 1.85) and we are finishing in 2K.
I have honestly heard conflicting opinions, even though the stats would lead you to believe that Epic would be a better way to go. I'm more interested in the thoughts of those who have first-hand experience rather than conjecture.
Could you not shoot UHD ProRes on the Alexa or for that matter 6K 2:1 on the Dragon?
In the case of the dragon given that you are shooting green screen, the final aspect ratio wouldn't have to be the same as what the dragon is shooting although I guess it depends on what you are up to. You would need to make some tests going down that path I guess tho.
You could always switch down to 5K when you definitely need the 1.85.
Anyway I don't know what you are up to but I thought these might be things worth thinking about.