11.5 is on the cusp of needing a wide.
Also, waist width only tells part of the story. The point where the inserts lie is wider than the waist. So two boards with the same waist width might be different width at the inserts. So while one board might feel too narrow, the other might not.
I couldn't tell you how wide the two boards are at inserts. Maybe you might be able to dig up info. My buddy who has a size 11.5 boot doesn't have problems riding my boards or other regular widths. He's had boots from 32 and K2 (current).
You can probably go either way. It's either going to be slightly too narrow or slightly too wide.
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