To compare the size of frames you should look at the effective top tube length and headtube length. This will give you an indication of the reach and height you can get the bar to. With a road bike as long as you can stand over the top tube with your feet flat you have enough crotch clearance so the reach and stack height are much more important.

As road bars don't have rise you need to make sure a given frame and fork combination will allow you to get the bar high enough in relation to your seat height. You can use stems with some rise but there are only a few options with much more than seventeen degrees of rise, particularly for the over sized handlebars that are standard these days. If choosing between two models that have a slight variation in top tube length you can compensate with a longer or shorter stem. A point to bear in mine is that carbon steerer tubes can only be spaced up around 30-40 mm before you risk damaging it. Too high and you risk the fork snapping off while riding.

carbon mtb rim

carbon mountain bike rim

carbon road bike rim