I'm 5'11" which is classified as a medium by the industry standards, however I can use a large with a short stem and suffer with the more technical trails but make it up on the longer and less elevation cross country terrain.

It all depends on body proportions also and preference of size. In this case the stem is long so I do believe a rider up to 5'9 would work, again it's the riders preference.

 "2006 Norco Fluid One size small (fits someone up to 5'9"-5'10" however I had a ton of fun on the bike and I'm 5'11)"

When has a small fit someone 5'9"-5'10"? That's usually bordering between a medium and a large.