A couple of points: First, the 5K iMac isn't a "professional workstation" by most measures. In particular, it doesn't include ECC RAM or a "pro level" GPU. I w

A couple of points: First, the 5K iMac isn't a "professional workstation" by most measures. In particular, it doesn't include ECC RAM or a "pro level" GPU. I wish ECC would become ubiquitous across all PCs, but it looks like the industry is stubbornly leaving that as one of the few real "pro" differences. That's not to say you can't do serious work with a regular PC, just that it's not considered sufficient for high-end engineering and science tasks, where a flipped bit could mean disaster. The specs of the Mac Pro fit the bill for that, along with workstations from other manufacturers like Dell and HP. Since all but the "pro" GPU are also server components, prices shouldn't go up appreciably, and in fact will probably continue to slide as manufacturing techniques improve. High-end PCs will remain affordable, the components used for them have many uses and will be mass-produced in large quantity for the foreseeable future. One interesting area is displays, where it's hard to see smallish (48" or less) 4K TVs not encroaching on the computer display market heavily.