Hats off to MS on this one, the whole migration from XO to XOX seems well thought out for a change.
I bought a 2TB Firecuda 2.5" Drive with a USB 3 enclosure (ASM1153e chipset) to transfer my existing games on the XO, the added bonus (as already evident) is the loading performance of games has been significantly reduced, and some games like Destiny, it's quite evident in-game where the inventory icons load a damn sight quicker..
Be interesting to see if the Internal HDD on XOX is any quicker than the original or if External HDDs still offer a performance benefit.