Which computer company builds the best workstation???
I'm not an expert on Rambus, but it has implications on why many of the intel machines seem to really be limping. Rambus does not appear to be optimised for the data packet size that is normally found in PC's therefore there seems to be a big difference between "theoretical" and "real world" performance of the system. Cost is also a major factor, RDRAM is much more expensive to manufacture than DDR SDRAM. (by the way, the theoretical performance of 266 MHz DDR (Double Data Rate) SDRAM is 266 x 2 or 532 MHz) a big part of that cost is lisencing fees to RAMBUS corp. You can find RAMBUS cheap now because everyone including Intel is phasing it out and selling it at a loss. I would not buy it because it will be hard to come by in the near future.
Check out Tom's hardware on the web, they can give you much better explanations and comparative benchmarks for various chipsets and video cards etc.