Did you know that PA regulations mandate that the shortest amount of time between chairs on a lift, be they fixed grip or high speed, is a minumum of 6 seconds? I have never timed it but I would assume that most resorts run their chairs as fast as they can.
Six seconds yields an uphill capacity of 2400 skiers per hour, assuming no stoppage, on a quad chair (a triple chair would be 1800 skiers per hour and a double chair would be 1200 skiers per hour). Not that they may not exist, but I've never seen a resort list a capacity on a fixed-grip lift that would indicate running the lift more than one every six seconds. Five seconds would be awfully fast. On top of that, there's probably some engineering constraints regarding weight loads and spacing on chairs that makes more than once every six seconds problematic (in addition to the potential increase in skiers getting swatted by chairs in the loading area). That regulation does put a bias on future acquisitions of those six pack chairs, though, doesn't it?