Well that did not take but a few posts to have some one disagree with my first ever post. Here's one way of looking at frame sizing:
Performance/training/racing - if fitness and comfort/position/fit allow go as small as you can, max out seat post, longer stem if needed, slam stem if flexible and need for more aero positioning or deeper bars and drop, thus getting a shorter wheelbase, quicker, snappier and lighter bike. Think sports car.
Comfort/touring/endurance/centuries/commuting - by all means get a bigger frame for the longer wheelbase, cushier ride, less quirky performance, better comfort, less drop and reach cockpit, for medical /comfort/fit problem needs. Think SUV or Caddy.
But more often than not, when you see a clyde on a bike (trying to go fast versus farther?) the frame sometimes is way too big and they actually may have been able to go smaller. Some tall riders getting into the sport think that since they are tall they have to buy the biggest frame they can find. Not necessarily true and that was the purpose of my post.
Closing comment - hell of a lot easier to sell a large frame (59/60/61) vs. an xl (62/63) or xxl (64+) frame size and a lot easier to find 60's than 63's. But always buy and ride what fits and feels right especially if that makes you happy and keeps you riding.
I'm 6'4" with a 37" bicycle inseam (36" in trousers) a 62cm bike works just fine for me, I've thought about going smaller since my current top-tube is only a 59cm c-c and the seat tube is 62cm.
The geometry changes as you change size though, and also varies between brands. I'd recommend getting fit by a professional bike fitter before buying, they'd point you in the best direction for your size.
Let's face it, once you are over 6 feet tall, no two of us are proportioned the same.
If you're looking for an old steel bike, you should be fairly theft proof by riding a jumbo-jet sized frame.