Gems, fatigue and increasing magic levels

[Corwin]

Ygorl said:
No single spell will ever put you over 200 fatigue. You can cast a spell with a fatigue cost of 700, with no gems beyond those intrinsic to the spell, and you'll still be alive and at 200 fatigue.

Are you absolutely sure about it? I thought mage would refuse to cast 700 fatique spell, unless you would give him extra gems(above spell cost) to reduce fatique, or he is much higher than spell's level, or you make him cast it in the communion, et cetera.

I am not sure about it though, haven't tried it for a while.