The real-world differences between asm.js and PNaCl are really not that big (basically only whether threads are true POSIX threads, or WebWorkers). Here's a (shameless plug) demo page which has the same demos as emscripten and PNaCl compiled from the same C++ code (warning: most of the PNaCl demos need the latest Chrome Canary): http://floooh.github.io/oryol/