Hi

A good starting point is https://en.bitcoin.it/wiki/Mining_hardware_comparison where you can see some MH/s in different card models

Also the speed of a cpu in Hertz is just the clock speed, nothing more, the GPUs give more hash power because are designed to do specials calculations for games, also this calculations are better to brake hash in a cryptographic way.

Also the software used to mining implies difference in MH/s because some tweaks using different flags according to your card model.

When the combination, card + miner + flags (combinations) are good, you will get a very very good speed from your card to mining coins

Hope help, Im a newbie tooo