Gizmodo did have a video showing the speed increase which unfortunately seems to have been pulled. We’ve imbedded it below just in case it re-appears but the general gist is this: don’t expect a night and day increase in speed.
In loading the NY Times website in Mobile Safari, the new iOS version shows a decreased loading time of a couple of seconds when compared to iOS 4.2.1. Not a massive difference, though any speed increase is obviously welcome!
UPDATE: iSpazio has now got another video which shows marginal to significant speed difference between Safari on iOS 4.3 and iOS 4.2.1 when browsing different websites: