As a 5D III owner and I tried 6D for 2days.
When compare to your current t3i
1. 6D = better high ISO
2. 5D III = better high ISO, more precise AF, and better ergonomics, ok fps
3. 1D X = better high ISO, more precise AF, super ergonomics, and top-speed fps(you get to delete more
4. 7D II = no real spec, weak rumors, especially no hand-on, therefore no comments.
If soccer is not a primary reason, then I vote for 6D. It's great FF for entry level, portrait, and candid. You will see huge improvement in IQ and higher ISO.