It sounds as if you are looking for very fine interpolation between way points, and sending the result over a rather narrow link. Would it not be preferable to send the waypoints over the link and have the Arduino interpolate for you? Sorry if this is a daft suggestion - I have no experience at all of what you're trying to do - but the design just feels rather back heavy to me and I suspect it'd work better if you promote some of that work to the front end processor.