Ishikawa Tutsumu (石川 温) of the nikkei shinbun has an article up where he was able to test an iPhone 4S. He did 30 speed tests in Shinjuku, and had no significant difference in speed. The 4S got an average of 1.39 Mbps, while the 4 averaged 1.26 Mbps. These two results are statistically indistinguishable, and there were of course cases when the iPhone 4 clocked faster results. He didn't specify the uplink speeds, but an image he uploaded shows about 150 kbps.
This is because, even though the iPhone 4S supports 14.4 Mbps, where the iPhone 4 is limited to 7.2 Mbps, the network is the bottleneck. This should come as no surprise, since no one reports getting anywhere near the theoretical maximum speeds on ANY Network in Japan. Put an iPhone 4 and 4S on Docomo's FOMA network and I bet there will be on average no difference in downlink speed.
SBM can push the angle that the iPhone 4S will be faster on their network than on AU's, but in real life, the opposite could very well be true, especially in underground and mountainous areas. Mr. Ishikawa was unable to test an AU iPhone 4S.