I got interupted and skipped some of your questions. Sorry.
>1. Are they really better at hygenic behavior to reduce the mite threat or is this an exaggeration?
The SMR's are. I haven't had their All american lately.
> Do they even have mites in that part of Texas?
Yes, they do. They also have AHB (Africanized Honey Bees) in that part of Texas.
>2. What kind of bee would I get if a superseeded queen mated with my Italian or ferel drones?
From my recent experience, I'd say viscous. But you could get lucky.
Probably they will still have some resistance to the mites.
>3. How well do they overwinter?
The SMR's I had didn't stay around so I don't know, but my guess is fine. The All Americans will do just fine.