So while the e8400 offers the best price/performance, the e8500 is a much better overclocker at only ~15% more cost. Unless you were willing to spend 270 dollars on the best C2D around, I personally would recommend the e8500 for the combination of price and performance. You will easily be able to reach 4.0+ ghz!
The 9550 would be a great CPU for me if it was only cheaper. Currently puts me $100 over budget.