The people at the store are correct:
1. The stock cooler is all you **need** to run programs, games etc.
2. Prime 95 is not a program, it serves no use whatsoever other than to put unrealistic loads on your CPU. It's not recommended for Haswell CPUs except under manual voltage control due to the presence of AVX instructions which can spike voltages.
3. They told you it would be all your need running at stock speeds but you are not running at stock speeds.
On a side note, the HX850 (10.0 performance rating) would have been fine for your needs and is much better PSU for overclocking, the HX1050 (8.5 performance rating) has some issues, notably voltage regulation and ripple suppression, so it may limit your OC a bithttp://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=245
A short stint at 99C won't cause immediate damage to the CPU but continued hi heat and / or voltage will reduce its longevity