I'm mostly replying regarding the notion of putting the EXE on each workstation:

I'm not a big believer of that. Although, I don't know for sure, but I would expect much if not most of the EXE gets sucked into memory at the git-go.

Also, what speed is your network? Ours is 1000 mbit and maybe yours is only 100 mbit and not any slower.

I think the biggest slowdown is unoptimized queries. That said, you might not be able to optimize everything in the app and you might be stuck with some slow performance as the DBFs get large.