Top tube length has barely been touched upon here. I am currently riding 3 road bikes. A 52, a 54, and a 56cm frame. I am comfortable on all 3. The 52 and 54 frame have the same length top tube and I have the same length stem on both of them. The 56 has a longer tt and I have a shorter stem on it. The stem on the 56 is only 60mm long. I must have longer legs than normal for my height. It seems that most large frames have short top tubes and small frames have long top tubes. Most of the middle range frames have almost square dimensions. (54/54, 58/58) My 52 has an almost 54 tt. Your body proportions can have a major bearing on what size frame you will be comfortable on. Several fellas on this forum have stated that they ride a frame that they cannot stand over because they have a long torso and like the long tt. Many of the fellas say they like to see the front axle behind the bars when riding. I like to have the axle in front of the bars. If you are looking for a very areo position a smaller than normal frame will be required but you had better be flexable or you will not be able to ride very long. TRI bikes allow for an areo position but most of them have real steep seat tube angles to help the comfort level in the areo position. A good fit for someone six six is probably hard to find and if one is six six with short legs a good fit is probably available only from a custom frame shop. I am sure there are some tall riders on here that will have a much better feel for this than I. Good Luck
My 27" Cannondale ST800 is a 27" frame (68.5cm c-c, and 73cm to the top of the seat collar) and it has a 62cm top tube...
Typically really tall people are "taller" in the legs than in the torso. Although I'm 6'7" and when I sit down I'm not as "tall" in terms of of torso height. Obviously still taller than a little person, but torso height isn't quite linear with height. So while bigger frames have top tube lengths that might fit someone smaller, a Clydesdale cyclist still needs mongo wide bars (WTB mountain dirt drop bars which are 60cm wide not 46cm) and will struggle with their bigger hands on most drop bars without a double or even triple roll of bar tape (or old tubes under the tape).
Essentially it sucks to be a big cyclist because nothing fits, and everything feels wriggly and flexy as its designed for 150lb spanish climbers. Then again, we were able to dunk, and that was was pretty cool...