AMD strictly moderated (AMD)

[mmoy]

If you look at that site that was posted last night that allowed
you to compare performance between a wide number of Intel and
AMD processors, you'd see that the 4400 beats the 4600 about
as many times as the 4600 beats the 4400. And on a lot of
benchmarks, the results are very, very close.

This would indicate that the extra cache outweighs the advantage
of 200 Mhz in quite a few benchmarks and shows that access time
to memory is a very important factor. Which is why I feel very
comfortable with my purchase of the X2 4400 as the best chip in
the lineup for the money with dual core. And which is probably
why there is no 4000 chip as I suspect that benchmarks would
show that it is overall comparable in performance to the 4200.

Of course you can get an Opteron at the X2 4000 level but
finding one at retail is near impossible.