I've noticed a very odd bug. In RtI, the Native infantry (all kinds) absolutely butcher the framerate. When there's no native units on the map (or you're not zoomed into them, the sprites don't effect the framerate), performance is excellent. I can't remember the name but a Native cavalry unit armed with muskets that the British have doesn't hurt framerate at all, though. It's really weird but not that big of a deal once you get into the meat of Episode 3.