Last time I researched, which was about a month ago, this is how it went in order of best:
1. Best P4 with PC1066 (fastest) RDRAM (expensive)
2. Second best P4 with PC1066 RDRAM
3. Third best P4 with PC1066 RDRAM
4. Best P4 with PC800 RDRAM
5. Second best P4 with PC800 RDRAM
6. Best Athlon with best DDR
7. Third best P4 with PC800 RDRAM
8. 2nd best Athlon with best DDR
9. Best P4 with best DDR
....
And so on. That's a generalization obviously, but that's pretty much how it was. Athlon doesn't use RDRAM at all, not sure why they don't I just know they don't have an option to use it.
I'm guessing the list is about the same now, but I couldn't tell you with out looking around a bit.
So in general, the best P4 with the best RDRAM will kick the pants out of the best Athlon, but the price difference is also monstrous. Of course then you could step down a rung or two of the P4's and still beat an Athlon for closer to the same price.
Which is what I did.
db (dee bee)