I don't think performs is the correct term but I believe T-Mobile doesn't pay to have roaming. So regarding that, your Sprint phone will likely work in more places than T-Mobile.
A phone that has a 16 core processor and 8 GB of memory seems to be a little extreme to me. They are also rumoring it will have a foldable 4K display which would be cool. Also have a fast charge which says can charge your phone up to 40% in just 4 minutes. If these rumors are anywhere near the final product, this thing could still be amazing.
http://www.techtimes.com/articles/111776/20151129/samsung-galaxy-note-6-rumored-to-get-16-core-chip-8gb-ram-microsd-slot-and-4k-screen.htm
In addition, especially Tmo, they are still burning through cash as well. The only two that won't slow down due to financial reasons is AT&T and Verizon. But as Robert said, stay tuned...