I didn't use Zalmans thermal paste. I bought Arctic 5 silver for it. I'm sure the Zalmans would have done alright but Arctic 5 silver is the best thermal paste available. Ya 3.4ghz is a pretty sweet OC on a E6400. Alot of overclocking has to do with your mobo as well. I probally screwed up when I got mine the Asus P5E seems to do alot better overclocking. Thats were the clocking mainly lies how far you can push your FSB. All the cpu cooler does is keep it colder to give you a higher window as far as temps go. If you knock 10C off going aftermarket thats 10C more you have to up your Vcore and push it further.