also it’s easy to work out if an emulation is CPU or GPU-bound. just run top command in SSH when you’re playing them – if it says ~25% cpu use. it is using 100% of one core (almost no emulators are multithreaded) so likely isn’t GPU-bound. in my experience this was always the case with the pi2, but i’ve not tried it on the pi3.
Actually if you run top command and it uses more than 1 full core it shows more than 100% not more than 25%.