OK. I answered your other post.
Now, with more information ...
65 C is not a bad load temperature. Go into PC Health in your BIOS and set the thermal alarm to 70 C. However, 54 C is kind of high for an idling temperature.
Next, you have probably reached the limits of the stock heatsink.
There's a good chance that with 4 DIMM's, you will need to relax the memory timing and/or increase the RAM voltage a little to get the system to run stably.
Running a program like Orthos or Prime95 does two things. It puts a 100% load on the CPU - something that seldom happens for an extended period of time in normal operation - to check the core temps. It also checks how stable the system is by performing some really complex calculations.
There has been a lot of discussion here about how we should stress test. It takes less than 10 minutes to drive CPU temps to their maximum. Computronix (http://www.tomshardware.com/forum/221745-29-core-quad-temperature-guide)
is our resident expert on Intel thermal management.
People stress test for different periods of time: 2, 4, 6, 8, 12, or even 24 hours. I test my overclocks for 24 hours. I used to test for 12 hours, but one time I just let the system run overnight and next morning discovered that Prime95 failed at 14 hours. I regard system stability as very important - not necessarily critical because I am not running complex, life-or-death calculations on my systems.
Here are two under $50 heatsinks that are pretty popular:
Sunbeam
http://www.newegg.com/Product/Product.aspx?Item=N82E16835207004
Xigmatec Dark Knight
http://www.newegg.com/Product/Product.aspx?Item=N82E16835233029
They both require a somewhat different approach to applying thermal compound.
Suggestions for applying thermal compound:
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=170&Itemid=1&limit=1&limitstart=5
And they are pretty large, so they might not fit inside your case.
Overclocking is a balancing act between CPU temperatures and voltage limits. I generally reach voltage limits before I reach thermal limits.