I5 6600k Temp

Although your ambient at 65F (18.3C) is well below normal which is 72F (22.2C), if you added the 4C difference to your "100% load" temperature of 38C, it would still only be 42C.

So the obvious question is what are you using for "100% load"?

Here's the recommended operating range for Core temperature:

80C Hot (100% Load)
75C Warm
70C Warm (Heavy Load)
60C Norm
50C Norm (Medium Load)
40C Norm
30C Cool (Idle)
25C Cool

"Load" or "100% load" or "full load" are terms that get tossed around the Internet like Gorilla poo in a cage. Since everyone tests their rigs with different hardware using X stress software at Y Ambient temperatures with Z measuring utilities resulting in CPU or Package or Core temperatures, it's impossible to compare apples to apples. This is why processor temperatures are so confusing.

There are only three relevant values; Ambient temperature, Core temperature at steady-state 100% workload, and Core temperature at dead idle. Applications, rendering, encoding and gaming are partial workloads with fluctuating temperatures which aren’t suitable for thermal testing or accurate temperature comparisons.

Intel tests their processors at 100% Thermal Design Power (TDP), so for owners who want to perform a valid thermal test, the goal is to replicate Intel's test parameters. Prime95 Version 26.6 Small FFT's is the standard for CPU thermal testing, because it's a steady-state 100% workload which runs Core 2 processors and Core i variants with Hyperthreading within 3% TDP at stock settings. This is the test that Real Temp uses to test sensors.

Core i 2nd through 6th Generation CPU's have AVX (Advanced Vector Extension) instruction sets. Recent versions of Prime95 such as 28.9 run AVX code on the Floating Point Unit (FPU) math coprocessor, which produces unrealistically high temperatures. The FPU test in the utility AIDA64 shows similar results.

Prime95 v26.6 produces temperatures on 3rd through 6th Generation processors more consistent with 2nd Generation, which also have AVX instructions, but do not suffer from thermal extremes due to having fewer transistors in a larger Die with greater surface area, and a soldered Integrated Heat Spreader.

Please read this Sticky: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

Pay close attention to Section 13 - Thermal Testing @ 100% Workload.

Download Prime95 version 26.6 - http://windows-downloads-center.blogspot.com/2011/04/prime95-266.html

Run only Small FFT’s for 10 minutes.

Use Core Temp to measure your temperatures - http://www.alcpu.com/CoreTemp

If you follow the Guide then you'll find your valid baseline Core temperatures.

CT