Are you buying used? Or just different sites/stores that only have one size? I find it odd that the sized are different prices unless you are buying them from different sources.
Anyway, the 2cm difference isn't a huge deal, so if the $50 is a big deal to you then the 160 would be fine. If it were me, I'd rather pay $50 to get the board I felt was best. But if your budget is a concern I wouldn't worry too much about the extra 2cm.