I have 10.5 Kaijus and can fit into either binding. I used to prefer L/XL Forces because I could run them straight out of the box, without adjusting anything, whereas I would have to tweak the M/L pairs a bit before they fit the boot right.
The Atlas has a longer basetray than the Force, so I opt for the M/L on that model.
I have a pair of the new Teams, which are running the same Stage 4 base as the new Force. I got the M/L and they fit fine. I'm sure I could fit into a L/XL without any issues as well, but running a smaller basetray is ideal for me, so I won't have any toe/heel drag.
Your call. You can fit into either of them, but might as well spring for the M/L.