DDR is a lot cheaper than RDRAM, when building your own box DDR is probably the better choice, more options (mobo's, cpu's, ...) versatility and price/performance comparision, but RDRAM does perform very very well. It outperforms PC133 SDRAM with over 300% on server and workstation configs. Anyway if you are going for a general purpose or game box, go for CAS2 DDR. DDR is becoming faster almost every day. For a workstation RDRAM is very nice. We have an early P4 1800Mhz DELL workstation with PC800 RDRAM and it's doing it's tasks very smooth.