Considering my budget, I have narrowed my choices to the followings:

- Intel Xeon X5660  2.80GHz     95w   6 cores  ~ $1000 (new OEM on Ebay)
- Intel Xeon X5650  2.66GHz     95w   6 cores  ~ $850 ( new OEM on Ebay)
- Intel Xeon E5649  2.53GHz     80W   6-Core  ~  $780
- Intel Xeon E5645  2.40GHz     80W   6-Core  ~  $560
- Intel Xeon W3680 3.33GHz    130W  6-Core  ~  $600
 
X5650 and X5660 are more expensive but ES versions (engineering samples) can be found on Ebay for lower prices. I wonder how much risk is in buying ES? Your experience/opinion?
 
 E5649 and E5645 are quite less expensive. What do I loose with them comparing to X line of Xeons? Do they over-clock better? II know they have lower QPI. Does it make a significant difference in their performance?
 
W3680 has a higher default clock speed at the price of higher TDP. It gives the impression of an already over-clocked Xeon. I imagine because of the high TDP, it has less over-clock capacity, right? Does it have a benefit?
 
Your inputs are appreciated.