This is an odd problem I've been having. When I'm just the Avatar, I move at blazing speeds around the map. Every time I added a new party member, though, my movement speed would decrease. Now that I've got the full 8, I'm crawling around. Is this normal? Is there any way to fix this problem? If not, are there any benefits to having a smaller party?

Unfortunately, the game lags with more people on the screen. There's not much you can do to get around it. Britainia Castle with a full party is the worst. Having a large party is better early on, but if you complete the expansion sidequest the Avatar is strong enough that you won't need much help from NPCs. The downside is you'll have to play most of the game to get strong enough to finish it.

If you are playing on normal (not exult) version, you can adjust the dosbox speed by CTRL+F11 (slower) and CTRL+F12 (faster).

It helps a little for the lag