The hope of every game engine is to make the CPU and GPU run as fast as they can, and this concurrency of speed allows you to have faster frame rates in your game. I will be the first to admit that I could use my CPU and GPU cycles better, and spending a few years on optimizations would certainly yield returns more indicative of the AAA titles you mentioned, but even those would strive to use the full power of your GPU.
The purpose of the motherboard and peripheral hardware is to run safety at the highest possible speed, and driver settings exist to ensure throttling is reduced when temperatures go beyond the safety point. I'm not 100% sure but the Ti versions were slightly overclocked to produce marginally better performance, but this should not account for overheating as the overclock is modest. I am guessing you have not modified the rig to be overclocked beyond the manufacturer's default limits, so the best guess I can make is that your noisy fan is the rest of fluff and other air-born particles clogging the fan(s). My recommendation would be to 'carefully' clean with an anti-static solution the main parts of the inside of your PC, including GPU and case fans, then get some software which can report the temperature of your main components, and determine your safety temperatures. At the same time, you can get free software to report the utilization of CPU and GPU across your system, and run this side by side with your AAA games and GameGuru so you can make a side by side comparison. If you have time, perhaps you can create a small hand-held video showing starting GTA V running on HIGH, then put the camera near the fan, and then launching GameGuru and likewise move the camera microphone near the fan so I can hear the difference.
Also as some calming information, a noisy fan is not a sign of trouble, it's actually doing the job it was designed to do. Dust can make it noisier but hearing it is actually a good sign when running your GPU at maximum. I prefer to use silent fans whenever possible, as they have the ability to run at max RPM without producing a noticeable sound outside of the case. Hopefully some of the above were of use.
PC SPECS: Windows 8.1 Pro 64-bit, Intel Core i7-5930K (PASSMARK:13645), NVIDIA Geforce GTX 980 GPU (PASSMARK:9762) , 32GB RAM