The US advantage
In the end the US may have a clear advantage here as their legislation on Kerb Crawling means that pedestrians generally are less bold that elsewhere. Sooner or later that will emerge as a benefit as the risk profile may be lower for autonomous vehicles at any speed.
The issue may also be what your comparitors are. if you are a driver comparing autonomous it does not make much sense, but if you are a non-driver comparing autonomous cars against buses or even suburban rail there is a speed benefit. Good to remember more than a third of our population cant drive.