SkierOfEast wrote a review of Arc'teryx Velox Crew - Short-Sleeve - Men's on January 13, 2014
Fit: Runs large
Ordered this shirt because I was happy with the Arc stuff I've got in the past, and I wasn't sure about sizes... most shirts I'm either a large or a medium now, and went ahead and got a large to hopefully be able to wear it as a 'daily' shirt instead of just for workouts (tighter fit etc...). I'm 5'11", 180 and in decent shape for reference.
The large was too large for me in this case, and I think a medium would be decent for daily wear and a looser fit at the gym or out hiking. I'm still experimenting with Arc sizes because they have different types of fits, but in this case the large was too large and was really baggy on me. But beyond the fitting issue, the shirt was light weight, had a stretchy kind of fabric, and was pretty soft and smooth, although I wouldn't pick the work 'silky' to describe it. Given the right size, I think this would make an awesome shirt to wear around.