I had the same bindings and boots a couple of years back. My Lashed was a size 10 and it was a tight bit. Lashed boots are really wide. I would suggest you move up to a Large Cartel if you decide to keep them boots.
Any particular reason why? You think it'll limit riding in any way?
I know I prObs should go up but it'll be a massive hassle to do so. If it won't affect my riding I'll keep them despite the tight squeeze.