I'm considering purchasing a Turbo of some sort in the near future (most likely a base or X). I'm 5'6" male, would the small or medium frame be better suited for me? Doing some googling gives me conflicting answers...seems 5'6" is around the cusp of the two sizes?
I have a small X. I'm 5'7 and the small was the only one I could stand over (short legs) with clearance. You lose the cool swooping top tube...but fit is way more important than looks. I think I need to get a slightly longer stem to give me just a little bit more open cockpit (don't try to accomplish this by moving seat back). The small fits me near perfectly. The geometry is dialed in really well for an upright commuting riding position.
I am 5' 6" and have a 2016 S. Definitely go small. The top tube is snug against my inseam when standing flat footed. There is absolutely no advantage to ordering a larger frame in my opinion as there are nearly infinite things you can do with different stems and seat tubes if required. That being said I like the stock riding position although it is a tad too "sporting" for me at times. I am 48 years old and have given up sportbike type motorcycles for specifically that reason. Even though it will look a bit less "cool", I will likely get an upwards angled stem at some point. The other option would be to have the bike shipped with an uncut steerer tube perhaps and use a lot of spacers, but I am not sure if Specialized gives this as an option. My bike came with about 30mm of spacers under the stem.
Check out my avatar and notice the higher bars on the X. Due to the suspension fork and slightly modified frame geometry the X inherently has a more upright riding position. I'll be 52 in July and have two fused vertebrae in my neck. I try to be very conscious of my riding posture - rotate my hips forward to keep my back flat and not arching forward, and try to distribute my weight between bar grips and seat. Good results so far commuting 27.8 miles (twice a day). I'm very sure I couldn't do it without the suspension fork and seat - I feel them doing their jobs when I need it most.
I'm 5' 6" and have the Turbo X in Small. Fits me fine and also my wife who is 5' 5", I wouldn't want anything larger. I am more comfortable in a more upright position and agree with New E Biker, IMHO there's stuff you can do to a small if it's too small, but much less you can do to a Med if it's too big. I am slim(ish), tho, at 60 Kg.