yeah 900 doesn't happen on and AMD Socket A board. It's just not possible. 400 is the tops unless you do some overclocking.
And whew, 600 System bus would sure be some insane sheeeit to see on and good socket A amd setup like that.
But yeah the reason AMD labels them like 3200+ is because it's roughly equivelant to a 3.2GHz Intel, depending on of course the exact chip of the Intel so the 2600+ is roughly equivelant to a 2.6GHz Intel. In some cases likes been said AMD will outperform the Intel and in other cases the Intel will win