I just measured really rough. 28", about 71 cm. I'm 5'7" with short legs.
I ride 175s.
I pedal through turns, even relatively tight ones (but not really tight ones).
Although I have a custom frame, I requested no particular BB height - it's about what they all are.
I can ride 170s too - rode them for track, and rode them on the road for part of the late summer, until I crashed in Aug. I used to ride 167.5s, for a long time, maybe 1989-95. I used to be much, much faster. Like 20% faster in the sprints. I used to be lighter (15-20 lbs from now, and I'm 25-30 lbs lighter than last year). I haven't done a max speed test this year, but I've done multiple long (30+ seconds - those are long to me!) efforts at 35-36 mph without standing, i.e. leadout/chase type efforts, not sprints. I just put an 11T on after not having one for most of a year, so maybe I'll go out and do some sprints at some point
I thought 170s gave me speed (back in 2008), so I rode them the year I wasn't working. I trained a lot, rested a lot, BFed a lot, and I did worse in races than normal (at my elevated weight - about 180-200 lbs). I returned to 175s and promptly did better in crits and such, with 1/3-1/2 as much training.
Now, lighter, with 175s on still (I put them on back in the early winter of 2009), I've had a great season so far. I've been holding off on going to 170s, but I may try it to get more speed. If, that is, 170s give me more speed.
I notice 170s vs 175s. I raise/lower my saddle height to accommodate the crank difference (5 mm). I'm most concerned with leg extension. The leg "rise" at the top of the stroke, not so much.
If someone raised or lowered my seat arbitrarily in a 10 mm range (+/- 5 mm) I'd notice it. I think most riders would too. I definitely noticed a 10 mm difference in stem length, and I noticed 5 mm in saddle fore/aft. 5mm in crank length is pretty significant. 2.5 mm, not as much.
I am more aero on 170s. Although my saddle is higher, my torso is more flat and I can hold a low position more naturally. Since my leg extension remains the same, my frontal area is basically the same.
To go to a longer crank effectively takes months, to raise the cadence back up, to learn to use the leverage effectively. I went to 175s because on my 175 mtb (2" knobbies, suspension fork) I was faster than my 170 equipped Giant TCR road bike (campy 9s). I went on to do very well on the 175s, but I was 210-215 when I was on the mtb, dropping to about 190 for the first races on the 175. For me long cranks make up for a lack of fitness and a lack of FTP. Since I lack FTP even when I'm fit, I'm not sure when/if I move to 170s.
But this is all me. Keep an open mind. I refused to try 172.5s back when I was on 167.5s, although I "tried" them for about 3 days. It took me 10 years go try longer cranks, and when I did, it made a huge difference.
cdr