Well, even though Rambus is clocked at 800MHz, it transfers the same as DDR, which is 1600MB/s. It is also said that Rambus has higher latency, but I can't back that up and would concider that a moot point for now. The reason that DDR on the P4 sux so much is that Rambus is implemented in dual channel, so it is effectively 3200MB/s. The I845 is only a single channel solution, so if it was dual channel, it could achieve 4200MB/s with PC2100DDR.
Now, I'm not AMD biased, as the P4 at 2GHz does beat AMD's finest at a majority of the tests. The AthlonMP (Palamino) O/C'd to 1.4GHz is able to keep up, but not beat the P4 2GHz (according to [H]ard|OCP's test). So, I'll imagine a Palamino 1.53 will match a P4 2GHz and maybe win a few benchmarks. AMD really should act fast as Northwood is right around the corner. Right now, Intel can't really scale the P4 higher on 0.18 micron, but once Northwood comes out, there's no stopping them until around 3.5 - 4GHz.