Moving to AT&T - Should I replace my N910T with a N910A - Band 29?

I am likely moving to AT&T from T-Mobile. Don't get me wrong, I am a very satisfied T-Mobile customer, but they have oversold their network in my neighborhood. Testing AT&T on a Nexus 6, I an getting 10X the speed, close to 40Mbps down when I may be only 2 or 3 with T-Mobile. So, here is my question: Should I replace my T-Mobile N910T with a N910A? I have read the N910T thread and I am not asking how wonderful the T-Mobile version is. I know. I don't root devices and I am stock on my Note 4. I don't care about unlocked bootloaders. Not important to me. I also understand less bloatware.

But when I test the Nexus 6, I get faster speeds, closer to 50Mbps. I am using Band 29 on the Nexus, Band 4 on my Note. I understand that the N910A supports Band 29. My area is congested. Will I regret in a year or 2 not having Band 29?

N910A => N910T via Reflash

Can this conversion be performed?

I.E. I buy an N910A (which is generally selling A LOT cheaper than a N910T via refurb sales), and reflash it with an N910T ROM (even Stock would do), and expect it to behave as would a N910T?

i.e. Could I get WiFI calling, and Band 12 on TMo?

Any directions pointed to would be appreciated.