Each screen update, the engine is only drawing the interpolation between two frames. Picking which two frames is not at all computationally expensive.
So lots of frames of animation is not a problem for the rendering speed, and only a consideration for filesize and RAM needed at runtime; textures tend to take a much bigger proportion of memory than vertices, so go add more frames to your animations!
Nobody is going to be upset that annex is a big download, since annex is a quality download and they can see a correlation between quality and quantity, right?
