I'm sticking with no VISIBLE difference - and I hope to be proven wrong (by the phone being much faster, as opposed to much slower).
I don't doubt that benchmarks will change, and the apps that measure system performance in milliseconds will see a difference. I just doubt that we humans will notice a difference in system speed. Yep, we'll have some cool new toys to play with, but I think that will be the main difference.
If ICS were so magical, then the Nexus would blow the Razr out of the water in day to day usage tasks. I think we all would agree that it doesn't...