I've read our starter motors draw about 120 amps at 12v. That seems pretty high to me, considering that equates to nearly 2 horsepower. So, all you need is 120 CCA's in terms of maximum output/flow. Any more than that (assuming the starter does in fact draw 120 amps) is like paying $10 for a $5 beer. There's no reason to do it.
The real issue in a battery is the total amount of energy that is stored, not just how much is released per unit of time. The important number is Ah (amp hours). That's the number of hours you could pull 1 amp out before it's depleted. If you have a 120 ah battery, theoretically you could crank your engine for 1 hour before the battery would be completely drained (of course your starter would be melted long before then).
Also, I'm a big advocate of deep cycle batteries. I'm so sick of running a battery down a couple times and having it effectively be worthless.
