RDRAM still out performs DC DDR at stock speeds.
Most overclockers will go for the DC DDR or wait for the Springdale chipset. DDR allows using a much higher FSB then people are reaching with a 850E RDRAM board, (about 150FSB for a RDRAM).
Here's a great look at Intel based chipsets,
Dual-Channel DDR SDRAM Arrives for the Pentium 4

Since Intel seemed to discontinue support for later RDRAM chipsets, many are going to DDR boards.