Jeez, and I thought I was the stem Nazi.

Some riders need spacers because they are new to the posture and need time to stretch and acclimate. Some just don't see the point of going lower than a certain point. And some need to ride a smaller frame in order to get a decent top tube length.

My starting point is with the brake hoods a couple of centimeters below the saddle. Above that, you might as well be riding a Townie.

A tip: as the torso becomes more horizontal the center of gravity moves forward. To avoid excess pressure on arms and hands move the saddle back a bit, and lower it a bit less to account for the extra stretch. And then, if you find yourself reaching too far, consider a shorter stem. But remember that most stock bikes already come with pretty short stems.