So I am about to do the 4,1 to 5,1 upgrade w/ a w3690 3.46 hex. I know on my mac pro3,1, I was advised to fill all the slots for increased speeds. I heard that to use my new ram @ 1333hz, I would only be able to use slots 1-3. How much of a performance loss can i expect using only 3 slots? vs 4 slots @ 1066hz? I feel I maybe misinformed also. If the speed differences are completely negligible, please inform me.