please take option for maximum heat output when torturetesting prime, the new version gives you the option.

"bald branch" :^D

open the side of your case, load the CPU, see how high the temp goes, 73°C seems too high in my humble opinion.

additionally you can run CPUMark http://cpu.rightmark.org/ to see if your P4 starts speed throttling (slowing down to avoid overheating) that way you are sure that the CPU is running too hot or not.

for config & demo of CPUmark check this article: http://www.digit-life.com/articles2/p4-throttling/