Crank length

I used to have 170s on all my bikes. Now my tri bike has 150s and I have a 145 crank in a box waiting to be put on that or another bike.

Tri bike shorter cranks can allow more aggressive fit.  Google and read as you will see wide variety of opinions. The difference between the standard 170, 172.5 and 175 is not much but that is what bike part companies think is ideal. Consider that those are supposed to fit people from 4'10" to men well over 6'6", does that make any sense crank length only changes so small.

I ended up calling my friendly LBS after being totally overwhelmed trying to find my own cranks.

Between gearing, bottom brackets, spindle lengths.. I got frustrated and let him pick out a new crank for me.

Ended up with 165mm Shimano 105, after a 172.5mm FSA Gossamer. 

Much better hip angle after the swap and some small adjustments.

I don't understand when people say they can't feel the difference in crank length. Either that or I'm a real princess and just don't put a pea under my mattress or I'll get even LESS sleep than I do now... Anyway, I digress. I can definitely feel the difference in crank length, even a 2.5mm difference.

I've got 175's on my MTB, 172.5's on my roadies and TT, and 170's on my track/single speed. I tried 165's on a road bike for about a week -- HATED them. Yeah, I felt like I could turn the pedals over at a slightly higher cadence (more like I HAD to with a slightly lower gear), but felt like I bogged down on hills too quickly.

I used to road race on 175's, counter to what most people thought was best at the time (170's were the most common size). I dropped down to 172.5's first on my TT bike, giving me a little more of an open hip angle at the top of the pedal stroke. Helped a lot with the low front end. I changed over the road bikes soon after for commonality.

Okay, with all that said, whatever you choose, likely the feel of the difference will go away quickly -- within a mile or two. Unless it just isn't for you, in which case it will likely always feel foreign.

My tri bike came stock with 175s and I rode it that way for several years, then experimented, first going up to 180, then back to 175, then 172.5, and now run 170mm cranks. 

I really LOVE the 170mm cranks. I can easily maintain a 90+ cadence while in aero with NO PAIN in the tendons in the front of my hips, which is what always happened if I tried 90+ with 175 or larger.  At 180mm even 80rpm rides would cause me pain in aero.  That was totally the wrong size for me, and 170 is totally the right size.

I am 6' and 32" inseam, btw.  YMMV.

Are the formulas you are using to calculate crank length designed for Tri position or road position which are quite different in goals of fit and position.

I can feel differences in crank lengths even of small amount and can adjust but the difference is there.

I get all mine on eBay.  A simple "dura ace 165" type search finds many.

i switched last year to a shorter length as well and am loving it bigtime.  not only on the bike but also on the run, legs just feel much better from the get go out of T2.