The Canon web board ran a poll of the best lens for Wildlife. The Canon 100 - 400 L IS won by a Huge margin.
http://photography-on-the.net/forum/showthread.php?t=59931

I only just now noticed that the Canon 70-300 is only F5.6. You're right - need something faster than that. But there is another Canon lens that is faster in same range - so many choices. Fortunately, have plenty of time.

A Bad day at Sea is better than a Good day on Land!