Oh my.
If you're running a single case fan then that's the issue.
You need at least two fans, one large fan to suck air in at the front and one smaller one at the rear to exit the warm air. The idea behind this is that it creates positive pressure within the case which, given decent cable management will help draw air over the components.
I too run the same Zalman cooler on my E6600. The thing about Zalman coolers is that they don;t usually cool a greater deal better than the stock one, maybe a few degress but they get away with being a good deal quieter and very sexy to look at. Their are more effective cheaper coolers on the market, the artic freezer pro is a good example but it is ugly as all sin.
Now to address the main concerns. 65C IS NOT EXCESSIVE, a lt of folk seem to think it is. If it's being measured from the temp sensor located under the CPU socket then hell yeah it's hot but if it's the T Junction sensor inside the chip then that temp is a little above normal but nothing to get freaked out about. The simple way of telling if it is overheating is to find out yourself. Boot the computer load test it and then give the top of the CPU cooler a little touch. If it's comfortable to touch then you're good. If it's boiling then you got a problem getting rid of the heat.
What you need to do.
- Get positive air pressure inside the case, upgrade the intake fans make sure you have at least one intake and one exit. With the intake at the front and the exit at the rear. Make sure that you also install the fans the correct way round as installing the exit fan the wrong way round will cause the warm air to recirculate around the CPU cooler. If possible try and get four fans going. Two intake, one at the front, one at the side, one exit at the top of the case and one exit at the rear.
- Manage those cables, wire bundles trap heat and big lumps of badly managed wires can actually create heat, but that's a whole different problem. Tie them up using cable ties and tuck them in to spaces create a clear path for the air coming in the front to get from the front fan to the rear exit fan.
- Thermal paste, there are a million different people that will give you a million different ways of applying it. I am not gonna tell you how to apply it other than practice. Apply the paste, press the CPU cooler down then remove it again. If you have even coverage over the CPU and the cooler base then you've done it right. Clean the paste off and reapply the same way. If you have an gaps you don't have enough or your CPU could have a slightly curved heat sink. Now you can lap your CPU to get rid of any defects in the CPU cooler but that's a huge pain in the ass with potential for all levels of disaster. Just experiment with the thermal paste to see what provides the best coverage just try to use as little as you can get away with to give decent coverage. Oh and the brand or type of thermal paste means nothing. I've used Artic silver, interl thermal pads and zalmans own thermal paste and the temp difference is 1 degree at most.
- Don't waste your time with water cooling. It's expensive it's something else that needs to be maintained, it's something you need to know what you're doing with and unless you're doing some serious OCing the advantages are no where near the cost and time you'll lay out trying to get a decent cooling ring set up.