i can tell you there is really only 1 important issue...
Heat due to Speed. all the other choices listed are either unimportant or silly (who's crying about chip surpluses or who is making you spend big $$$ to buy the latest cpu???).

i'm still using a p3 to do most of my desktop computing.
the problem is heat & power consumption. w/silicon based technology, the manufacturers are rapidly approaching the limit as to how many transistors they can cram onto a chip because of the heat generated. it will near the point where unless they can use an alternative material such as diamond, they will hit a wall.