Top tube length only relates to fit after considering the seat tube angle (how far foreward is the seat cluster "angled" relative to the BB).

You also have to consider the stem length (where a steeper haed tube angle favors a longer stem to preserve steering response).

So, different head tube angles (as may affect chosen stem length) and seat tube angles (as moves the top tube fore and aft) are pertinent to any top tube length decision.

As far as relaxed rider position, a lower pedaling torque might have the rider falling foreward unless the rider's weight is moved rearward on a more layed-back seat position.
A racer on the other hand is pedaling harder, so a more-foreward rider position will counter the pedaling torque so the rider doesn't have to pull themself foreward especially on steep climbs.
The more-forward position allows the rider to be more aero with less need for a sharp bend at the waist (which can limit power).
A more-foreward saddle position also makes for a quicker, more effortless transition from seated to standing, perfect for quick jumps and attacks on rolling hills and switchbacks.


Longer rides mean lower pedaling intensity, so no surprise that Merckx "Century" model frames have a more layed-back seat tube angle as the only change from their standard Corsa Extra.

I do mostly fast road rides between 25 and 80 miles at an average speed of 17-20mph. As such, I prefer an aggressive rider position but with a relatively high bar and a stable steering geometry. Examples of my preferred fit are shown below. The top bike is 72X72 degrees, with a 110 stem, while the bottom bike is barely 71X71 degrees and as such needs a wider bar to control the steering using the same 110mm stem length.
Surprisingly, both bikes are also super-comfortable for all my local "utilitarian" riding, as the foreward rider positioning with higher bars is a great benefit here where it is quite hilly.

I recommend a larger frame size when selecting a frame with a more layed-back seat tube angle, both to extend the top tube and to allow for a comfortable handlebar height.

The saddles shown are level at the front half. The rear portion kicks up but is soft enough that the ramp is quite subtle.
And my arms do get tired riding these on the longest rides, but the forward positioning also spares my legs (which is ultimately what always limits my endurance).

Lastly, a racing bike may have a slightly steeper head tube angle, longer stem and shorter top tube (in combination) to allow the rider to more safely draft the rider in front of him/her with less chance of touching wheels.
The bikes shown below are not built this way, they are touring models set up for fast riding on fairly technical road surfaces, so optimal drafting is of somewhat less importance. The auxiliary "safety" brake levers are important on these bikes to allow periodic "rest riding" with hands at the upper position. I only ever ride the hoods when charging uphill, out of the saddle.