I had a whopping 15 second negative split between my halves in the Fifth Avenue Mile today, yet it felt like mostly even-effort with a strong finishing kick in the last 350m. But when I worked out the quarter splits using Google Earth elevation rise/drop, and JK's formula for effect of gradient, it seems as if even-effort should make for about a 10-second negative split.
Assumptions: JK says a 10 foot drop saves you 1.8 seconds. I'm going to guess that a 10 foot rise costs you 2.6 seconds.
The elevation changes by quarter in feet are
[-18, +24, -31, -5] (for a net drop of 30 feet)
so the effects on quarter times are
[-3, +6, -6, -1] and on half-mile times [+3, -7].
I've run this race many times, and this makes sense to me. I wonder what other competitors think.