I have ceiling fans in my barn, but not above the horses stalls, but along the centre aisle, 4 in total spread down the barn. they are high enough that if a 17.3hh horse decides to rear (has happened on occasion) they still have lots of head clearance. So not sure how well that would work on a barn w a low roof.....These fans are good for circulating air, but don't really cool things down
I also have 2 large industrial fans that we use in summer at either end of the barn to push air. They are awesome....before that we used to give each horse there own fan on their stall as you described. But i found it always a pain in the ass to set up and take down, so when we purchased to 2 larger fans i thought to myself why didn't I do that sooner!
This past summer I still set up a box fan for our Mare w foal as our summer was so hot, and w foals not being able to regulate their temperature felt this was necessary to ensure they were both getting adequate air movement.
The large fans we have at either end of the barn are on all day, and depending on temperature at night shut off when we do our barn check. If temp doesn't go down adequately we leave them on.
Horses are like chips...you can never just have one