I used to have an Asus Z7S-WS dual LGA 771 platform with (2) Intel Xeon E5472 chips and 8gb of DDR2-800 FB ECC memory. It was a pretty great machine. If you can pick up that board or the EVGA SR-71 boards since they are some of the only models with the 1600mhz FSB and great PCIe 2.0 setups, then I'd say go for it if your i7 build prices out for a lot more. The downside is that for more modern software in single threaded configurations, you will lose a ton of performance.
That machine was able however, with an AMD 7950, to run Crysis 2 in ultra with everything cranked to max on a 1920x1200 monitor.
so in short, multi-threaded apps = win
single threaded apps = not worth it.
A good way to build a modern machine if you have a budget constraint, look up open box parts on Newegg or go used on Ebay and Amazon. You can often save upwards of 30% for perfectly fine parts. I'd stay away from any type of used storage medium though.