I added another stick of DDR3 toward the end of it's generation on my X58 build because the 6GB I was using was not enough. I happened to find the same Kingston HyperX, but the timings were not quite the same.
When adding RAM it's best to find a module that is pretty much identical to the RAM you're using in brand, model, speed (frequency) and timings. There are 4 timings listed and the one that's most important is the first one (CAS), because it's the one that determines how many CPU cycles lapse in between each passing of data from RAM to CPU.
The fastest, most efficient way to run RAM is in dual channel mode, and in this mode each channel mirrors one another to increase speed. This is why dual channel RAM is sold in matched modules that are measured to be in very close spec to one another.
You can get by with higher timing numbers, which is slower RAM, but it can affect stability until you lower your RAM timing settings in the MB BIOS. This is because your PC will default to the slowest timings of your RAM. I had to do that on my last X58 system, but I also found out I didn't have to go from triple channel to single channel like I thought. It was an odd configuration, but my MB allowed me to run it in dual channel.
Let me know the brand and model of RAM you're using, preferably with timings, and I'll see if I can find a match. DDR3 is getting harder and harder to find, and can be fairly expensive for what you get, especially if it's high performance modules with low timing numbers.
The timings should be listed on your packing slip if you still have it, or the RAM container if you still have that, or the manufacture's website if you know the exact product page. As a last resort, it's also usually on a sticker on the module itself.
The reason most say to put Windows in High Performance mode is they don't know the same can be achieved in the Nvidia Control Panel under Power management with the Prefer maximum performance setting. The reason it's better to do it that way is your CPU only ramps up to it's boost clock speed when the game is launched. Then when you exit the game, the CPU goes back down to idle speed automatically.
In Windows High Performance power mode, your CPU will run at max speed all the time, generating unnecessary heat and wear and tear, and causing it's fan to run at higher speed. I (and I think most) prefer their CPU to run quieter and cooler at idle, which will also make it last longer. This is why Balanced mode is recommended by Windows.
The only caveat is you need to make a profile for each game in Nvidia Control Panel setting the Power management to Prefer maximum performance for any games you're having issues with. It's very quick and easy to do though and only need be done once with each game. People saying to use High Performance power in Windows are either naive, lazy, or running an OC speed constantly.
Yeah if you're only running the stock CPU cooler 80c is normal, but anything 80c or more is still considered fairly hot. The stock coolers just aren't very efficient. For about $33, or much less on a sale, you could get a decent cooler that would keep it at more like under 65c, barring abnormally high summer temps, etc.
https://www.amazon.com/Cooler-Maste...hyper+212+led&qid=1565031635&s=gateway&sr=8-2
The case looks OK, but if ambient temps are high, I would add the optional 2nd 120mm fan to the front.
I would avoid RAM optimizers, they are often not what they're cracked up to be. You can achieve the same thing just by restarting your PC before a game session, or using a standby list cleaner. All a standby list cleaner does is make sure your standby RAM is free to use. IntelligentStandbyListCleaner is the one to use, and it's very easy to use. It will also continually free up RAM during a game session.
https://www.wagnardsoft.com/forums/viewtopic.php?f=5&t=1256
That said, if a reinstall of your OS has fixed the problem before, there may be something you're doing (or a app you're using) that is causing system file corruption or even malware problems. It's possible as well if you're adding programs back in when formatting the OS, it eventual gets to a point where too much RAM is being consumed, especially if you have a lot of startups
I advise you first check for malware, then run the Windows System File Checker (sfc /scannow). CCLeaner and Malwarebytes are two trusted and free tools to clean your PC of possible malware.
CCLeaner
https://www.ccleaner.com/ccleaner/download
Malwarebytes
https://www.malwarebytes.com/mwb-download/
Refer to the MS support page on how to properly run sfc /scannow in W10. Pay close attention on how to restore the system image first, as you need a healthy system image file to run the scan properly.
https://support.microsoft.com/en-us/help/4026529/windows-10-using-system-file-checker