This has always been a problem for me. I am short,only 5'4". My first road bike was a Motobecane with a 19" frame. Definitely too tall and to long a reach on the drops. Now I have a Schwinn Cruiser Deluxe with a 19" frame. Maybe 1/2" clearance. But it has worked out OK doing emergency stops. My other bikes are a MTB and a hybrid. With the smallest frames and sloping top tube I have maybe 1 to 1 and 1/2". This I feel comfortable with. But I have held off on a road bike because of the level top tube. Today I put money down on a Specialized Seqoeagh or however you spell it. 47CM frame with sloping tube. Maybe 2" clearance and the fit is perfect. So at 2" over the top tube I feel like there is absolutely nothing to worry about! Having been off a road bike for almost 10 years and now my first one that fits it is like something totally different. I have done 35 to 50 miles on the Schwinn so a century on the road bike should be easy as it has a granny chainring and weighs half of what I am used to. Hills,here I come.
Dan