I had the opportunity to test this out just the other day. I built up a 48 frame for my daughter, while I ride a 51. When I took her new bike out for a shake out ride I was perfectly comfortable on it with the saddle height adjusted for me and could've ridden it the whole day that way. Next week I'm going to visit my son in Seattle and he has my old Davidson which was sized the old way with a horizontal top tube vs. the current sloping ones. After I had my current bike built I felt that this bike was slightly too big even though the frame was custom built for me. I'll see how it feels.
As an aside, I'll have to visit Davidson's shop with my '81 bike. The last time he saw it, he looked at it completely puzzled because the graphics were a mix of his old style and newer ones but that was already over 20 years ago. After he built the frame, Charles Hadrann from Wright Bros. Cycles added all the components. His shop is now just down the street from Davidson's. And these guys must be old! I'm 67 and they were older than me when I had this made. But maybe not that much older since I was just 26 and anybody that was 30 seemed old at the time. Now we're just a bunch of old farts.