The only place I feel safe enough doing a full sprint is on Zwift and it gives to the benefit of better aerodynamics than I can probably manage on my own.
That being said, I can do 700 watts in the drops for 45 seconds and I'm a terrible sprinter out of the saddle. And that's probably good for 33-34 mph.
I doubt I can do much better. My FTP is up from about 245 to 285 over the previous three months but my top end has gone basically nowhere. Apparently I did 900 watts for 15 seconds in June and I still have no idea how I managed that.