Originally Posted by rufus
5'9 3/4", 79cm(approx 31" inseam) here, and i ride a 52. custom measured and built for me by Antonio Mondonico.
but it's got a 54.5cm toptube and 12 cm stem. my torso and arms are a bit longer proportionally to my legs, so that's what i ended up with. my old Specialized was a 54cm with a 54.3 cm toptube. fits me just fine, but i have absolutely no standover.
i think the most important measurement when fitting is toptube. if you feel too stretched out or crunched up, you're not going to be comfortable. seat tube and standover should be secondary.
Top tube length is only one factor within the larger picture of "effective reach" and frame fit. I am of similar height and with a similar sized frame, although with a 130 stem. I almost went with a Mondonico so I know that his STs are steeper than average, the results of which is an increase in effective reach. At normal seat heights, reach increases about 1cm for every 1 degree increase in ST angle.
One of the things that should be given consideration in terms of choosing a smaller frame, is handlebar drop. With a smaller frame comes more exposed seatpost and a shorter head tube. The net effect of combining these two factors is a larger drop to the top headset race. This works out great for a fit rider who rides with 8cm to 9cm of handlebar drop, as it allows for adequate drop with the need for minimal spacers. Each cm of handlebar drop increases reach by a little over .5 cm so everything with the smaller frame tends to work out, including putting a rider in a more aggressive riding position with good front/rear (45%/55%) weight distribution. For a less fit rider there will be a need for more spacers and possibly a riser stem.
As an aside, I'm wondering if he slacked your seat tube to give you that extra cm of TT length.