E7200 temperatures won't drop

My E7200 (Intel's stock cooler) has the problem that even when running without overclocking, the temperatures are about 45 *C / 113 *F idle and 65 *C / 149 *F under heavy load. I've tried reseating the cooler various times, and I've replaced the standard paste with Arctic Silver 5 (using the official Arctic Silver instructions), but nothing seems to help.

The ambient temperature is a bit high because of high room temperature and Club 3D 4870 Overclocked edition producing heat inside the case, but I'd still like to see the temps go a bit lower.

So I've been thinking about getting a new cooler, preferably one that'll do even if I decide to overclock. I've been thinking about Noctua NH-U12P, but as the price is quite high, I was wondering if you could recommend something a bit cheaper. That is, if there are any cheaper coolers worth looking into.

Additionally I'd like to ask about overlclocking the system. I've tried it a bit with the highest possible multiplier, then increasing the FSB. At some point the DDR2 frequency rises so high that the system won't boot (I can't lock it at 800 MHz, I can only adjust CPU / DDR2 ratio). Is this the overclocking limit of my system or is there something I can do to make the system boot again, for example can I safely increase DDR2 voltage and will it have any effect?

(MB: MSI P35 Neo, Case: Antec Sonata Designer 500, PSU: EarthWatts 500W)

You can't OC with temps that high.

Here is about the best you can do for price, performance, and good installation. Requires you to remove the motherboard though:
http://www.newegg.com/Product/Prod [...] 6835233029

This one does not require you to remove the MB, but you may have trouble installing because the clips require your fingers down under the cooler and heatsinks around the cooler may block your fingers. More of an issue with P45 boards.
http://www.newegg.com/Product/Prod [...] 6835207004

I just looked over your board, and I would say that's a go on the Sunbeam. You don't have large heatsinks.

As stated, higher overclocks are going to require RAM capable of more than 800Mhz.