I actually have an epic campaign with a Wiz6/Ftr8/Sps13 in it. Using an extrapolated version of that strange 1st to 10th-level prestige class, I have recently given him Channel Spell IV.
He usually (read:always) uses a quickened true strike followed by four channeled lesser sonic orbs (from the same book). That is a Huge amount of damage. That player also uses Power Critical with his masterworked mercurial greatsword (beefed up by a greater magic weapon spell) to do silly amounts of damage.
Lucky for me, as the DM, he can only do it once per day, which means that I usually throw in a lot of disguised-looking-more-dangerous-than-what-I-am-creatures/NPCs at the group to flush out that dangerous attack, not to ruin any climatic fights later on.
But I think it is a great concept, but it does make the ranger and the fighter envy him sometimes. But as a wizard, he is pretty non-descript at these high level games.