I've got extremely long legs, 39.2", but I did of course grow up with 175mm on MTB's and 172.5 on road.
When I got more serious with biking, I went 180mm, as it just makes sense for a big guy to use big cranks. The 5mm difference is barely noticable, it's that minute. Big guys should be able to get 200mm from Shimnao, but that's a different league of discussion on it's own.
Last year, sping, I entered a training camp and got to test a road bike with 175mm's. Bike fit me like a glove, I was very content to be riding it....everywhere but up. I would roll backwards on moderate climbs, it seems. And I normally love climbing. A few years earlier it had been okay on my spare mtb riding huge alps in France, but now I'd been spoiled too much I guess.
My MTB's all have 180mm, my road and commuter bikes, most SS, 175mm, and it works. I must say that I once had 185mm's on my road bike (still have the cranks), and that was fine as well, just required a lower cadence. I'm only not using them in fear of pedal strikes. I hit my MTB Eggbeaters on the tarmac last week, Surly Pacer, 28mm tires, 175mm 105 Octalink cranks.
None of my 175mm crank'd bikes will now climb worth crap for me, but I can tolerate them on pavement.
I have no trouble spinning 180's, then again, my huge legs aren't natural spinners anyway.