^Hourly capacity= (3600/per second dispatch rate)*number of people a train can hold. Green Lantern is just over two minutes long, but let's assume 2:30 just to be safe (actually, this is the length RCDB has listed). This means that, running two trains, the capacity of Green Lantern is at least 672 per hour. However, with a third train, the MCBR is located about 90 seconds into the course. If the trains can dispatch right as the MCBR is cleared, the capacity is increased to 1120 per hour. Riddler's Revenge's has a duration very similar to GL's, but has a higher theoretical capacity due to having 8-car trains. SFGAdv may need their third train more in the summer months, but SFMM definitely needs the third train in the winter months; SFGAdv can manage 90-150 second dispatches, while, during the winter months, SFMM gets about one train loaded every 4-6 minutes.
When I visited in August, all three trains were running, and were being cycled very consistently. I believe the ride was being run to its full capacity, whether it is 1100 or 1500. Right next to GL, Superman had to deal with 4-5 minute dispatches with two trains. I can probably say that there will come a year when SFMM will need their train more than SFGAdv does. Maybe now now, but this will probably be true a few years down the road.