well if the chipset is an i850 or one of its series then the motherboard will need RDRAM yes...but the P4bs have 533fsb and do not need RDRAM.
RDRAM is QDR (quad data rate)
DDR SDRAM is well DDR (Double Data Rate)
as for the optimization, its based on the chipset - which basically defines what your getting on the board in this case what memory its using. So the i845PE or one of its many MANY cousins (I think the PE is the latest incarnation) uses DDR, so you would find motherboards with that chipset, where as if you wanted RDRAM, you would look for a i850 system, I think the i850e is the latest although I havent been keeping up with 32bit RDRAM so im out the know with what chipsets etc, it uses (so if anyone wans to tell me here go for it )