There is a great guide on TH, http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guide
Most E's can clock quite high, but I would definitely recommend an aftermarket cooler. The stocks do the job of cooling a stock chip, but they're not much good after that. Depending on what type of OC you're going for and you budget, there are a number of great aftermarkets out there. I use an AC Freezer 7 on my Q6600 @ 3.4Ghz, and it keeps my temps under 60C, and it's cheap.