AMD PR ratings have generally been about on par with the similarly rated Intel, but the truth behind the 2400+, so on so fourth, is really the same speed as an Athlon Thunderbird.
If you remember back, they used to make Thunderbirds. Well a 2400+ is supposed to be as fast as a 2.4GHz Thunderbird would be. However, like I said and it generally turns out, it's about as fast as a similarly rated Intel. (PR:Clock)