What's your top speed?

What are realistic speeds at Herne Hill in a sprint?

I've used my speedo a few times but it didn't have the sensors so it was using GPS which spike a lot and not that accurate for sprints and stuff. It had spikes of 44mph occasionally which I know are totally wrong but also some more leveled spikes of about 33/34mph, are they realistic speeds?

38mph in a sprint is good going for Herne Hill. I've gone over 40mph indoors (just).

[Both based on Speedo top speeds, I have no idea how!]