I'm now a small?

I'm thinking of getting a wetsuit to do some real swimming in the Massachussetts ocean this summer.  Doing some internet research, I find that I'm now a 'small/tall' size.  And I'm on the bottom of the weight range for 'small/tall'.  [On the other hand, the imperial and metric sizes don't line up here, so maybe this sizing chark is just wrong...and I'm still a M using standard US male clothing sizes.]