Yeah I wear a US size 8 boot (shoes are 8.5 or 9) and the waist width on my board is about identical to the waist on the 151 cm board you're looking at. I wouldn't want it any thinner than that. Sounds to me like a 151 would be the right fit...
Does burton have any demo days coming up at your local hill? They just did one last saturday at Lake Louise and my girlfriend tried a few different boards. She's in her second full season now and she said it was great to try different camber/rocker profiles, different bindings, etc. If you can meet up with one of them it's be a great way to try before you buy.