The 5DII IQ is hands down better, especially at 400+ ISO, but the 1DsII is no slouch either. The 5DII will still be my main camera and the 1Ds will be my back up or when AF speed is a must. The AF and shutter response of the 1DsII makes me giddy. The shutter lag of the 5DII bites me in the but with sport shots. You can really see the difference in the AF accuracy of the 1D bodies when using fast lenses. Plus they just feel so awesome in your hands. When used 1DsIIIs come down to about $2500 I think I'll pick one up.