Dave above, rruff and I explained the problem with stack and reach. Stack and reach came about due to the conundrum of frameset mfr's when compact geometries which btw are a good thing...were developed. When this occured, seat tube and head tube lost their proportionality. This is key. The reason why seat tube length was used for years and that 99% of riders can still fit on frames with 'virtual' seat tube length = .667 X inseam is seat tube length was always proportional to head tube length with horizontal top tubes. But frames rarely have either straight or horizontal top tubes...nor even 'virtual' proportionality between seat tube length and head tube length with the advent of endurance frames with longer head tubes. This is when virtual and effective sizing became available. At least with the latter, there is some sense of saddle position unlike Cervelo's stack and reach. With virtual or effective top tube sizing...effective top tube length is the imaginary line from the seat post centerline to the steerer center along the top edge of the head tube. This is still better than stack and reach. So you want to know who does it right? Specialized does. Make no mistake, frame mfr's have been conflicted about frame sizing for some time. This includes Look and a few other mfr's who sized their framesets center to center which confuses so many.

So is there a bottom line or summary in all of this which leads to so much confusion on the 41? Yes as I have stated all along. There is no silver bullet or single metric for frame sizing that works. A frame's fit has to be taken in totality. That means:
1. length of the top tube
2. height of the head tube
3. seat tube angle which determines the critical horizontal distance from sit bones to BB center for proper weight distribution on the bike. When you push the saddle back on the rails or opt for a different seat post with greater setback because of Cervelo's wacky fixed sta's, reach is affected which isn't reflected in their 'definition' of reach....unlike typical 'effective' sizing which is top tube measurement from center of seat post to center of steerer long the top of the head tube. This is how Specialized, Trek, Giant and several other mfr's do it.