Are there geometrical differences between framesets optimised for flats vs drops, other than top tube length?
If the effective top tube (horizontal measurement) is OK for you - then the only other things I can think of might be the head tube angle &amp; chainstay length. A road bike may have a steeper head angle &amp; also have shorter chainstays. Which quickens the handling &amp; steering. 
Mind you, at the smaller end of the road bike sizing - the head angles tend to be a little slacker which helps with toe overlap. So head angle also depends on size.

Best thing to do is a compare a few geometries from a manufacturer for hybrid and road. There isn't a hard and fast rule for geometries. 

Also consider spacers as an alternative to a riser stem - might save you a few pennies.