Sprinting speed depends on the course going into the sprint, gradient, wind, and rider. A strong sprinter will hit virtually the same top speed given the same course and conditions, and, in a strong headwind, similar jump point.
The slower the sprint starts the better the jump the sprinter has to have. However a sprinter with a strong jump will be up to top speed pretty quickly. Uphills and downhills really affect top speed - As a general rule I'll say that a fast uphill sprint may hit about 30 mph, a flat one 40 mph, and a slight downhill one 50 mph. Wind is super important - 10 mph more actual headwind means you will be going 10 mph slower in the sprint (if you're hitting the aero wall).
A leadout helps hit consistent top speeds but the real reason for a leadout is to give the sprinter an ideal spot in the field. Typically evenly matched sprinters will hit about the same top speed. This means that if everyone tops out at 42 mph then no one is passing anyone. This means that if one sprinter started from 2nd spot (due to a good leadout) and another from 4th spot (less good leadout and then surfed wheels to get 2nd wheel behind the sprinter) then the one from 2nd spot will beat the one from 4th spot, even though both are virtually identical sprinters.
Top speed is a red herring, a distraction. When I had my best top speed I couldn't come close to hitting it in races or I was too far back when I started my sprint (see the paragraph above). I've done consistently better when my actual top speed dropped 10-15% but I was a better all-round rider. Think about that - 10-15% is a LOT of speed - at 40 mph that's 4 mph, so if my top speed was 40 mph before now it's 36 mph. For the last 5-ish years I'm down about 20% from my best but I seem to do better in races due to other factors.
Relative top speed is important. In this race I did one of the faster sprints of any race that day but I had poor position so I didn't do well at all (in Strava it says I averaged 41.7 mph in the sprint):
Here's a poor position start but the sprint decides it anyway. Not ideal position but it works out. Uphill, not sure of various speeds, finished at 28 mph?:
Same course, ideal position, break dangling off the front, I'm less focused on winning than on beating Bryan while still placing top 7:
Finally if you get to the line in a sprint you should be able to
"throw" your bike. It's an easy thing to practice, I think it's fun, and it doesn't take talent or fitness or whatever. It's just technique, just like cornering and drafting. Free places, sometimes even a win (non-HD, 3rd person, same course as the two above):