Thanks everyone for the tips.
@luke2 I don’t think yours will work for me (or at least I didn’t see how) because the notifications aren’t tied to the page in any way, but thank you.
@vini_brito Yes, I had started moving to searches instead of filters but then some folks convinced me that filters would probably be better, especially when there’s more data to search through ( "Do a search for" vs. "Current User's list of things:filtered" (Again) ). Yes, more data means there’s more to filter through too, but not compared to searches (e.g. there will eventually be hundreds of thousands of notifications to search through, but each user will only have hundreds of notifications tied to them). I still don’t know which is right, but I’m sticking with filters for now, when appropriate.
@JonL Thank you, this sped things up considerably.
@JohnMark Thanks, this didn’t make a difference, but I could see it making a difference when the count gets huge.