Well, RD is PC-800 where DDR is probably only going to be PC-266(or 233), so the RD is a lot faster. I bought my PC in July(needed for school and as soon as I bought the price of everything in it plummerted so RD was out of the question. If you can afford to put RD in your computer I would strongly recommend it. You may also want to check out www.ibuypower.com before buying a PC. They custom build every system and are the cheapest place I've ever seen for building a PC, especially if you want something thats top of the line.