DarkSable :
You can easily go up to 4.5GHz with that chip and that cooler - as long as you're below 65 on 100% load, then you're JUST fine.
Like edo said, there's no point upgrading your cooler when yours is sufficient, when you get infinitely more benefit from upgrades elsewhere.
If you DO upgrade your cooling, going to another 'Fisher-Price' cooler is about the worst thing you could possibly do. Save up and get a real water-cooling loop, and you'll actually get performance, along with reliability and the option to expand.
I actually highly disagree with getting a real water-cooling loop unless you're doing an extreme system with very heavy overclocking and 3-4 graphics cards. 4.7-5.0.
Custom water cooling is becoming less relevant every year, hardware is getting more power efficient, and better. An all in will do 4.5ghz easily and stay cool. As cool as a custom loop is, it's unnecessary unless you're into for the look and fun of it.