Accu-stats used to keep detailed stats on this sort of thing, and years ago they started out focused
mostly on statistics, and put out a little magazine. To compile the stats they filmed matches.
Inevitably, they grew into a pool video company, selling those filmed matches.
Now they only rate the player's performance (errors and so on) in a specific match.
I think some videos don't even include the ratings anymore.
But! Several (all?) of the Accu-stats magazines from years ago were scanned and used to be available on this site.
Luckily the internet archive saved copies of these scans even though they're gone from azbilliards.
You can view them here:
http://web.archive.org/web/20120816035452/http://www.azbilliards.com/accustats/
More recently, AZ user "AtLarge" compiles break stats on virtually every major event and posts them here.
It's sort of his specialty. Just type AtLarge break stats in google,
and then add site:forums.azbilliards.com afterwards, to limit the results to this site.
Here's a shortcut:
https://www.google.com/search?q=atlarge+break+stats+site:forums.azbilliards.com
Off the top of my head:
The hardest depends on whether they have to keep it on the table or not.
Past a certain speed that's very tough.
Here's
Mike Dechaine breaking 32 mph (flies off)
and here he is breaking
33.5 mph (also flies off).
Basically, several guys can hit over 30 but it's risky.
Bustamante is famous for a big and very effective break.
Larry Nevel is famous for his monster stroke like table length draw 1 handed, and can also break over 30.
Yvgeny Stalev is a russian champ with a very flashy powerful break, he actually
hops on the table.
For number of balls made on the break, the most I ever heard of was 7 and the most I ever saw personally was 6.
For the pro who averages the most... I dunno but Shane Van Boening is worth mentioning.
He's famous for having arguably the best 10b break in the world. He makes the same ball very consistently
and often drops a 2nd ball too. In one of his strongest matches vs. Mike Dechaine,
he averaged about 1.8 balls on the break and Mike averaged 1.7 or so. Shane made 4 balls on 3 different breaks.
In the US Open, Shane made a ball without fouling 80% of the time.