Hum....I'm 9 or so inches wider then you. My first pack was in size Medium. I like them, but the bottom tabs were just reaching the landing zone and it seemed to ride low on me.
I'm right at that number where they say max for Medium is 36 in and Minimum for large is 37. I went with Large and they definitely are bigger on my, but still enjoyable.
My though is the Mediums will fit you like the large fit me, bigger, but not horribly big.
Hopefully someone closer to your size can chime in.