Have you ever considered swapping the stack-based VM in ChucK for a register-based one like the one in Lua 5 (
http://en.wikipedia.org/wiki/Lua_(programming_language)#Internals)? I switched to this design in ChucKJS, and it improved performance a great deal. I think it's much nicer to work with as well. I was thinking it might also ease eventual auto-porting of ChucK to JavaScript via Emscripten.