I ran some cocos2d examples on a weaker PC than the one in the question, running snow leopard through VMWare with sufficient FPS, but that's all i can say. I also remember running some stuff that was more GPU intensive than this on a Mac Mini, and than running it on the device. It actually ran faster on an iPhone 3GS, i assume it's because the emulator doesn't utilize the GPU, but i might be wrong about that one.
Hope that was any help to you :)
Other stuff to consider:
In anyway, you're really going to want to test your game on a device frequently no matter what, and not just because of performance related issues, but compatibility as well. When working with OpenGL ES (and not only!) often stuff that runs on the simulator won't run on the device and the other way around.
And another thing to keep in mind might be the most important one, assuming you're talking about some kind of an "action" game - getting your gameplay to feel right and intuitive depends alot on it being tested with real input, as opposed to simulating clicks with the mouse.