im right in the middle of binding sizes for 390 bosses. i think it would be better to go with the s/m because they would be light er and softer.
is there any reason i should get the l/xl if the s/m fit?
Do they actually fit? My experience with bindings that are smaller is that although the boot can go in fine, the buckles slip sometimes when you try to tighten them because they're right at the end of the straps. If you can buckle in with the boots on, without any problem, I think you're ok.
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I'm in the same situation...I have Flux supertitans and went with the larger size and they're too big. They do fit but the base plate looks like it's better suited for a size 13. I also have Union Force in the smaller size where my size 10 are at the high end and maxed them out and they fit perfectly. I say go with the smaller size.