Give me links to these tests. Because honestly I had 2.2.1 on my 3G and went to AT&T and did side by side with the 3GS and there was maybe 1/2 second difference.
Now that I have 3.0b1, next to the 3GS at the same store there is no difference.
Yeah I know that Apple says it is 2X faster on their website. If that's all you're going on then...
For one...
http://www.youtube.com/watch?v=HtWd312PMfs (not the best example)
http://www.theiphoneappreview.com/06/iphone-3gs-speed-comparison/