The Mac N64 emulator I use is Sixtyforce. Only for mac, but runs well. I've run the Starfox 64 and Rainbow Six on it with no problems (except keyboard controls are hard, but that's normal :P). It's free, but there's a full version that has a few more features and costs $16. I like it.
The speed is good, especially for emulating the N64 hardware with software. If you don't have a mac, that's okay. I think it runs as well as Mupen and PJ64.
<3 N64