I just traded my 50D yesterday in on a 1DsII. I have no doubt that the 5D series have equal potential in IQ given both are FF but until you handle one of these beasts you can't understand. It took me back to my days of shooting with my trusty Nikon F2 with drive. There are less bells & whistles like MFA, Live view and a smaller LCD but I was willing to give that up for the advantages of top line autofocus and metering and the build quality isn't even a fair discussion. Any body that needs an accessory grip is going to be at a disadvantage. The 1DsII is now selling for @ $2K and when introduced sold for $9 GRAND!!!! Yeah, it's worth trying one, you can always sell it easily if you find it too much.