High chance your CPU / GPU is throttling. First check whether you block your air intake or not. If no then I think you need to send it back to have a check up.

Yup, wear and tear.

My mindset is like this. FAN > CPU and GPU or CPU and GPU > FAN (Thats me though). So i set fan as max speed when gaming and set it to medium or low depends on the temp.  , fan is cheaper to replace i suppose than CPU and GPU. 

If the temp is ok then let it be if not set it up one level higher and check.

This i'm not sure. Need some one with experience to answer you. Though with some $$, they might do it. 

For me as long it is floating around 80 celcius, i'm fine with it. For yours, yup it is high temp for sure (by my standards anyway)

Different people different view. Of course the lower the better.

Well, i disable turbo boost and undervolt my CPU. Since the turbo boost doesnt seem to increase the performance in gaming that much.

Using Intel Extreme Tuning Utility. Easy to use. , Yup setting to 99 disable the turbo boost.

Lol, if you want to then download it then go to manual tuning, look for dynamic CPU Voltage offset and set it stage by stage (I go -25mV then stress test it for stability for 20-30 minutes after stress test is successful i further reduce it by another -25mV then rinse and repeat.)

Do note. When stress test (without gaming), you can undervolt more compared to gaming. So set profiles for normal usage and gaming.

Though the bad thing about undervolt is BSOD. There might be hidden risk so do it at your own risk.

The thing is i prefer them doing while i'm watching. You'll never know what they do behind close door (My 2 cents).

My temperatures are also high. Playing Cities Skylines even with the lowest possible settings and resolution causes it to throttle. For D2 not so bad I guess but occasional throttling also (3+ games, 1 throttle). I think I really need to repaste :/