Yup, iOS 6 and Siri work now. I'm happy with my 4S (and am trying to save a house deposit, so skipping the iPhone 5) so glad to see the 4S basically gets all the software changes the iPhone 5 has - means an investment a year ago (bought outright) lasts longer in terms of 'the latest shiny things'.
I have seen the geekbench results for the iPhone 5 that shows it's faster with dual-core, 1GB than the S3's quad-core and 2GB. That's the advantage of controlling all the hardware and software in the end - you can optimise everything. I expect if I used the 5 for any period of time I might find the 4S sluggish... so I'm going to avoid doing that as I'm happy enough with the speed of the 4S.
Looking forward to the 5S.
P.