BIF with D300/300mm f/4

I've been shooting this combination for a few years now, typically in manual exposure mode, trying to stay around f/8 as that seems to be the sweet spot. I usually use ISO 800 to keep my shutter speed above 1/1000 sec. However, I see that the sensor is better at lower ISO, and am wondering what AF settings other people are using. Any input would be appreciated. Oh, shooting Raw, too, PP in ACR PSE 11. Thanks!