The E8500 (@ 3.16 GHz) is the exact same chip as the E8400 (@ 3.00 GHz), only factory clocked slightly differently. One quick tweak in the BIOS of your motherboard and you'll have your E8400 at the same or faster clock than the E8500. You can even easily overlock it past the E8600 (@ 3.33 GHz), which is much more expensive. And this is on stock cooling! Although you will probably want to replace the stock cooling sooner or later anyhow since it's not exactly good (loud).
Man I got mine to 3.8, I originally had it at 4.0 but that only lasted 2 weeks before it got unstable