Rendering Processors: AR350 vs AMD vs P4?

landrau asks: "I'm planning on building a render farm and was wondering whether anyone would know the pros and cons of the AR350 processor, used in The Renderdrive, as opposed to building a renderfarm with an AMD or P4 processor." While the Renderdrive looks like a real rendering workhorse that can produce some gorgeous results (see images in page header), does it justify its lofty pricetag of £6950 (over $12,300USD)?