Thought I would bump this thread since I finally found the solution to my foot pain!
Turns out that for me, it was not the boot at all, but the bindings. I had a size 9 boot in a L binding, and after I stap my foot in, the boot would slide towards the outside wall of the footbed in my binding while I was snowboarding. This resulted in the whole outer section of my foot (from my pinky to about the middle of my foot) to get very painful and then eventually go numb. I bought some medium bindings, and I went snowboarding on them for the first time yesterday. I'm finally pain free!!
Thought I would post this incase anyone else is having similar issues...