In theory the 2.16 would be 8% faster. In reality i might be 1-2%. If you can try to get the 1st generation of Core2 duo's. The only deterent with the current 2.0Ghz is that it only comes with a combo drive (cd burner/dvd rom). I would get the 2.0 superdrive from the previous C2D gen.
If the money doesn't matter, then go for 2.16GHz. But to be honest, you won't notice any improvement, especially if all you plan on doing is relatively average, such as surfing the net, writing papers, and listening to music.