EDIT: ^beat me to it!
Some rides are obviously way easier to achieve the "theoretical" capacity than others, since most of the time the manufacturers theoretical capacity is an indication of what the ride is technically capable of, assuming dispatch interval is hit every time and with completely full trains. This number can be almost impossible to come near for some rides with complicated restraint systems, etc. For example just because the ride is capable of dispatching a train every 60 seconds doesn't mean it is possible with the limited number of crewmembers that some parks staff at their rides.
I know when I used to work at Nitro we could hit 1400-1500 pph if we were really hustling. Basically you dispatch the train in the station the moment the previous train drops off the lift. The lift always has a train on it and the trains roll right into the station without stopping on the transfer. It's a beautiful thing when a crew is pumping trains out like that. On other rides, this is not so easy. B&M hyper restraint design has a lot to do with it.
Some parks like Disney however, will very realsitically run the ride at its maximum capacity all day long, just because they have the staff and the appropriate planning/logistics/ergonomics of the ride system down to a science.