I started this project with a pulse generator based on a ADCMP606 CML-output comparator. It was faster than my scope at the time, so all I could really say was that the rise-time was less than 350 ps or so. Last night, I found some quality time with the new scope, and measured the rise time of that circuit at less than 120 ps.
Overall, for a $6 (single-quantity) part, it's not bad at all. I think I'm going to make another revision of this board and release it. With a 120 ps rise-time, it's certainly good enough for testing oscilloscopes up to around 2 GHz.