The beauty of the 1D4 is that you can set a min/max ISO setting. So if you don't want to go above ISO 6400, you can prevent it.
I might actually start using auto-ISO on this bad boy in situations where things are moving quickly and I don't want to mess with it. I've never used auto-ISO in the past but given my tests last night I'm pretty comfortable with the implementation on the 1D4 to start messing with it more.
Do you know how much crap I took for saying Auto-ISO was a extremely useful feature on the D90,D300s and D3? There are about 5 pages in one thread bashing me about it from about 10 different people.... :er:
Glad to see someone else has found the potential usefulness.