Out of interest, we ran some tests where we would continuously change direction 180 degrees in the exact same spot on the Xbox 360 with and without an install and then compared that with performance in the exact same spot on the PlayStation 3. Curiously, after repeating the process a couple of times, no matter how we ran Rage - even with no hard drive at all - the 360 would resolve prominent textures faster. In his mammoth Quakecon 2011 keynote, John Carmack talks about the fact that they max out onboard memory and that the split system/video RAM of PlayStation 3 in concert with the bulk of the OS caused some issues for them.
In terms of our experiment, the conclusion we have is that the 360 transcodes texture data faster, or it is able to cache more assets in RAM - either way, it's clear that there's more to individual performance characteristics than we know right now but id seems to be more at home with the Microsoft architecture. In terms of how this perhaps could influence gameplay, we're reminded of a couple of Wasteland missions where the player snipes at base guards from afar, ducking into and out of cover. On PS3, we witnessed some screen-filling texture pop-in as we hid behind a dune, which resolved much more quickly on 360.