I think the legitimate average schoolie size for most landlocked striper fisheries in the U.S. is 5-7 lbs. That’s kind of the no-BS real size of most stripers. For that size, giving you the ability not to get waxed by a bigger fish, I think an 8 weight is the best all around rod.
Me personally, I choose to fish a ten weight single-hander for stripers, but when I was full on Spey fishing for them, I did use a 7 weight. Spey and switch rods have a lot more lower blank space (aka “ass”) and thus you can move fish with them which are a class or two above what you would consider the top end feasible range of a single hand fly rod.
Good luck.
Zach