Bike Sizing Question

Road bikes are more forgiving from a fit perspective because there are less contact points.

I seem to recall Dan Empfield making some comments on ST over the years the he's far more comfortable with sizing someone down on a tri bike than on a road bike.  Try to search for some of his comments.  So opposite of your thinking here.

Road bikes tend to have longer top tubes for the "same size" bike (let's say a 56cm Cervelo P-series vs a 56cm Cervelo R-series).

Thanks for the reference to Dan Empfield.  I read a few of his articles and branched out from there.  It was a little hard to decipher because tri bike vs. road bike seem to have a few different principles with fit philosophy and it can be hard to keep straight which he is referrring to.  I also found this quote below based on FIST.  I am thinking I may have to go to a 120mm stem to make this work which I do not think would is to far out there to dramatically alter steering. 

Top Tube and Stem Length

Next, we dial in the correct "reach" to the bar, or horizontal fit. Proper reach gives you easier breathing, better neck and lower back comfort, and better weight distribution and bike handling.

Some will say that you can always adjust the reach with a shorter or longer stem.  To an extent that is true, however if you change the stem length too much it will dramatically effect the steering of the bicycle.  The stem is essentially the lever arm you use to pivot the fork.  If it’s long it takes a more concerted effort to turn it (or to be turned, if you hit an obstacle).  If it’s short, the bike will be twitchy and nervous.  It’s best to stay close to a standard stem length and get a bike with a top tube length that fits your body position.