As has been pointed out on various technical sites (search around the Waiting for 3.4 threads for someone's link), the only real amazing speed boost in 2.6.3 was on server-based stuff. 2.4.24 was faster for desktop computing uses.
Now, we're up to 2.6.5 and 2.4.26 so things may have changed, but 2.4 is still not exactly a slouch.
Yet anyway.