Just like to add that weight distribution is also something worth considering, especially regarding handling. I notice that road frames in larger sizes tend to have shallower seat angles than small to medium sized frames. Longer, larger torsos need more space along the top tube to get the centre of gravity right but at the same time lengthening the bike's wheelbase proportionality would make the bike's handling less snappy so a compromise is reached by setting the seat tube angle shallower and lengthening the TT a little.