Some old charts people posted on Prius Chat back in the day.
This one is for a 1st gen prius and I believe shows how close the prius was operating to the theoretical optimal rpm/load:
This was calculated vs actual mpg for the gen1 prius:
The "marathon" data points were using pulse & glide. I think they calculated the gen1 prius had ~500watts of fixed load powering all the computers and such (not including A/C) which is why it isn't very efficient to crawl around at 5mph.
Gen2 steady state speed vs mpg:
PDF describing the Gen2's warm-up stages:
https://web.archive.org/web/20100206...ence051408.pdf