My home machine is a i7 overclocked to the moon (4.0GHz unsure of model). My workstation at work is a Xeon W3530 @2.8 GHz.
The i7performs with 14 gig of RAM performs significantly faster than the much more expensive Dell Xeon machine with 6 gig of RAM. In my opinion, unless we are talking virtual machines, or some multi-threaded app, clock speed is still king. This is using a Nvidia gaming video card.
I spec'd out a Dell supported workstation with an i7, 8 gig of RAM & a medium levelgraphics card. The IT guy who ordered it thought he knew better... changedittothe Xeon, a Quadro 4000 (with 2 gig of video RAM!) & cut the RAM to 6 gig. Cost way more for less performance. But then maybe some day I will be assigned some project that requires rendering & animations that will start to use some of that video RAM.