and is there really that big of a difference between a
Intel Core 2 Duo E8500 Wolfdale 3.16GHz
Intel Core 2 Duo E8400 Wolfdale 3.0GHz
No they are the same 45nm chips and same amount of cache. You can easily overclock them both with an aftermarket cooler. I'd say get a decent cooler and overclock the the 8400. Sure its the same price as, ok a little bit more than, the e8500 w/the stock cooler but you'll be able to push your 8400 anywhere up to 3.2-4.0ghz depending on your cooler and how much time and effort you want to put into overclocking.