So I have a mid 90's bike, a 56cm frame. I like the bike for the most part, but it might be a bit more aggressive than I really want at this point. I have my saddle at 78.5cm and the drop between the saddle and bars is 5in (maxed out with the spacers using a threadless quill converter). Apparently, the stack is 53cm, the head tube about 13.5cm. Leaving aside stem options, if I were to look for a modern frame, would the bigger stack (like I see the cannondale caad8 has 57.3cm stack for the 56cm frame) and/or larger head tube be the areas where I would have the slightly less aggressive position? I am going to race in October and next season, but I like to do a lot of long rides as well. Anyway, just wanting to understand geometry a bit better so I know what I'm talking about if/when considering other options.

90's aint that long ago , the component companies are working to have something new that is the main difference.

'agressive' steep seat tubes & low handlebars .. old folks make different choices

seat tube angles , top tube lengths and steering . trail. are factors to consider..

I have a couple 90's bikes .. and some even older..

I have traditional steel bikes, with horizontal top-tubes and modern bikes with compact frames. I duplicate the key fit dimensions on all my bikes, so the fit is the same. I don't use spacers under the stem on the modern bikes, but my saddle to handlebar drop is not extreme.

"Geometry" hasn't changed all that much, as I understand it. Head and seat-tube angles aren't much different. If what you want is less saddle-bar drop, that isn't so much a question of geometry as of frame size. A bigger frame will tend to put you in a slightly more upright position because your saddle height has to remain the same (determined by leg length) but the head tube will be taller. So if I were you the first thing I'd be looking at is whether your current bike is, in fact, smaller than you'd like. Ride a 58cm frame and see how that feels.

Thanks, really helpful. At first I was thinking maybe I might need a 54 (mainly basing it on the competitive cyclist calculator), but was also thinking the same thing about 58.

A traditional frame is sold in more increments to get correct fit. A compact or sloping top tube requires fewer sizes to do the same thing.

About all the old geometry has going for it is tradition and more sizing.

Do you have a bike now? If so there are several ways to raise your handlebar, lower it, or extend the reach to the handlebar. Try those before you make what seems to be an arbitrary jump from 54 (if that's historically been your size) to 58. It's a big jump.