I'm 6.3 and XL was too small for me. I went with XXL Crosstrail and it feels like custom made lol
My guess is you should go with L-XL, but it also depends on few other factors, including legs and arms length and so on. Medium sounds way too small. My wife is 5.6 and her Crosstrail version - Ariel is perfect in XL.
Everyone is different and badger1 have also good points about that. Go with your feel, ride some and you should be able to tell if its the right fit for you.