My 3TTT quill stem seems to point slightly downward, and those are set around 73deg right? On the other hand I didn't feel the bike to be super twitchy.
Not necessarily. I have a stem on my track bike that does a nose-dive downwards.
Some of them had a radical down-sloping so you could set the handlebars lower than a conventional stem would allow, for a more aggressive / aerodynamic position. On the track it allowed you to be a bit more aerodynamic while still maintaining good arm extention and optimal bend in the elbows for a firm strong hold on the handlebars which was required in maneovering on the track. And on the road, well, in a time trials, these enabled you to go down even lower in that aerodyamic tuck.