…I think it’s pretty much “all there” in the thread title.
I figure this knowledge would come in handy if I a) Ever manage to visit Rome myself, or b) Want to “make a scene” while watching a romantic movie set in the Eternal City. 
Everything I’ve ever read, says that you can’t trust any estimates. It seems that gladiator’s were too highly paid to be allowed to be killed frequently, so it was a rare occurance. Generally, the accounts will give an estimate of the number of folks killed during some other guys reign, and not whomever the current Ceaser happened to be. So if you’re looking for a copy of the Roman Sporting News, ya probably ain’t gonna find it.
Of course, I fully expect one of our Doper historians to show up shortly after I post this and prove me totally wrong.