[thejeff]

No. A mage can only use one gem more than the gem cost. This increases his level by one for either fatigue reduction or to be able to cast the spell.

He can only do this if his level in the path is at least the total number of gems he wants to use.

Your version was prevailing opinion for quite awhile. I certainly thought so, but it was dis-proven in a long thread a few months ago.
If you can produce a counter-example, I'd love to see it.