A 56cm TT fits me perfect. (5'-11.5" 33 inseam)

im 5'11 33 inseam and i ride a 54 orbea, keep in mind that you really should be fit on the frame without going beyond a 120 stem. If you get the bike with a forward center of gravity it can be unstable and too aft you loose the ability to control. It does matter on the geometry of the frame though and all of the other measurements needed to fit your bike.

sorry man, but this ain't right. I have 5 bikes with 130mm stems, and one with a 140mm. If anything, the longer stems increase stability slightly because the weight of the bars and levers is a bit further away from the centre of the pivot.

There are gazillions of people, including plenty of taller pros, with 130mm stems, and they (the pros) have to fly down icey mountain roads at 90kph and sprint at 70kph+.

6'1, my track bike is a 60 with a 110 stem, and my cross bike is a 57 with a 115. Both of my bikes were fitted by professionals. I also use both for racing.

TL;DR entire thread.

If you can't be personally fitted for a frame/bike at your LBS, here are two things to use as a guide for a road bike frame:
stand-over height. should have a minimum of 1" between groin and top tube. Preferred is 2-4"
Top-tube length, should be: (your inseam x 0.67)

that's a good starting point.
Using that, I take a 48-50cm frame on most road bikes, or a "Small"
I'm 5'7" with 30" inseam.

Using inseam to determine top tube length is a really bad idea.

Not according to this:
https://www.wobblenaught.com/fittingsystem.asp

granted torso to inseam ratios can vary from person to person, as long as you're not a wookie, it should be a good starting point.

That sounds huge to me for level top tube frames. I'm 5'10" 32.5 cycling inseam, and the last frames that gave me that much room was both a 53 IRO and a 50 Fondriest. Both were horribly small. I'm now on a 57 Look with a very slightly sloping top tube that is just touching my bits. And an IRO mark V size 59 with a touch higher (level) top tube. Both bikes feel great and handle beautifully when ridden.

FWIW - I'm 6'3 and my custom Seven is coming with a 59.9 cm top tube based on their calculations.
I have a 35 inseam.

I'm three inches shorter than you and have the same inseam. A 60cm top tube for me is ridiculous. This comes from the old Lemond method which multiplied inseam by .67 to determine seat tube, which is much more sensible. Unfortunately, seat tube means a lot less than it used to so they're trying to use this in a way it was never intended.

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6'4" 60cm frame fits great.

but wasn't Lemonds idea of fit to stretch you out? and i thought at one point Merckx did the same

+1
All of my bikes thus far have been 60cm.

I'm 6'1 and optimal is between 57.5-58.0 TT

I'm pretty flexible and like to be a bit stretched out but 60cm is way too long on the TT. I ride anywhere from a 60-63 ST with a TT from 57.5 to 59 with 58 about optimum. You can't determine TT without knowing something about body proportions and inseam tells you nothing about that.

my old Nashbar road bike, CCroMo frame, traditional geometry, is a 21" frameset, or 53cm. That was OK when I was 5'8", but lost an inch due to some ortho issues over the last 20 years, and now when I stand over the bike in cleats, my 'bits' are resting on the top tube, which makes mounting and dismounting the bike very awkward.

On a side note, when looking at framesets for Kestrel and Kuota, I use standover height measurements from their geometry charts to give myself 1-2" of clearance, and oddly, the top tube lengths of their frames fall precisely into the lengths calculated with the formula I mentioned.. so I guess whatever Lemond was thinking, so were a lot of frame-makers.. even to this day. I seem to fit well on a "small" frame withabout a 20-21" top tube. This usually leaves me with a good saddle position, 165-170mm crank arms, and a 100-110mm stem @ 0 degree rise.

It is quite possible that I am a mutant however. I've been compared to worse. hehe