RE:Casting vs. Reeling Hand...
I had to read your post twice. I remembered you casting right handed with the spinning outfit. But after I you mention it, I also remembered you recording the data lefty. Funny I didn't pick up on that earlier. And I never saw you tossing a fly at the Dam. Close quarters no doubt.
I am a righty but have very good dexterity with my left hand as well. I can write and throw a ball with either hand but I'm not ambidextrous. But I definitely would not be comfortable fishing lefty. I would lose casting distance and accuracy not to mention missed strikes. I wouldn't be as comfortable playing (control) a big fish lefty either.
I don't know if this applies casting or not since I have never tried fishing lefty. But I am right eye dominant. Now I know if I tried to shoot a firearm lefty I will always be off center. My 11 year old son who is righty couldn't hit a coke can at twenty yards with his BB gun. Until I figured out although he is a righty he is left eye dominant. Once he learned to shoot lefty he can now shoot the lights out. Like I said I don't know if this is applicable. Just my .02