Steam / DirectX

The problem has been discussed on the Steam Forums. The problem is that each game has to have a binary-identical version of the vc++ redistributables. Since games link against different versions of these libraries, steam always installs them the first time as a safeguard.

Credit to mordi2k for finding the post
Here's a link to the Steam Support Article about it (forum post is no longer available). The text is quoted below.

Why does DirectX install with every game?

Running the DirectX installer is not a matter of making sure your overall DirectX install being up-to-date. Microsoft has a helper library with D3D called D3DX. You'll find binaries for this like d3dx9_43.dll in your Windows\system32 folder. There are over 40 different versions of the D3DX library for D3D9 alone, and many more for D3D10 and 11 as well. Each game that uses the D3DX helper library is linked to a specific version. As such the game must run the correct D3D installer version that it was specifically compiled with to ensure the binaries exist.

Even if a later version of the binary is already installed, that version cannot be used, and even if your DirectX install is up-to-date because you've run a more recent version of the installer that is not guaranteed to have installed all previous versions. Even worse, if a version is installed for x86 it doesn't guarantee the same version is installed for x64, so 64 bit and 32 bit games may need to run the same exact installer version but targeting different platforms when run.

Furthermore, Microsoft's licensing terms prevent anyone from distributing the files directly, the only way to distribute them is to run the installer, that's also the only supported method from Microsoft to check that the correct version installed. Trying to manually check for the correct versions is extremely complicated because there are numerous files that must all be present and individual system configuration options like dll search paths complicate the situation. In addition, the dependencies and required checks may change in each new version of the D3DX runtime. The code to check correctly and repair broken installs all exists in the installer and running it is a guarantee that the correct binaries will exist when you run the game and prevents lots of bad cases where a game would fail to launch with an obscure error if a windows install was either missing the correct version or somehow corrupted in the past.

Why don't Valve's Source Engine games run the DirectX Installer?

Games which don't use the D3DX helpers (such as Source engine games) don't require running the installer on first launch as they only depend on major d3d9/10/11 versions being installed. However, games that do use D3DX must run it as it's the only way Microsoft has allowed for distributing and checking the version info on the files.

So, considering the discussion in the comments, and my opinion, possible causes of the FPS drop and screen tearing for the specific game in question, CS:GO, would be (in order of likeliness)

• Corrupt configuration files on CS:GO. (OP already reset them, discarded)
• CSGO or Source Engine update issues (No updates were released at the time of the incidents)
• Busted drivers. (OP already reinstalled them so, discarded)
• Broken GPU fan, so it throttles down to prevent damage. (Op checked them, so discarded)
• Dirty GPU contats. (OP already cleaned the card, so discarded)
• Tweaking fps_max value. (Already done, discarded).
• Nvidia GeForce Experience causing issues. (OP uninstalled it, so discarded)
• Steam Overlay causing issues. (Op disabled it, so discarded)
• Windows update messing with OS. (Op stated that no updates occurred before the incidents)
• Nvidia HD Audio causing issues. (OP uninstalled it, so discarded)
• Busted Video Card (By OP's comment this turned out to be the culprit)
• Busted RAM (Unlikely)

At the time of this answer we don't have specific information about performance in other games, OP specified that the screen tearing was occurring on Borderlands: The Pre-sequel as well, but we don't have specific performance data. On the other hand Furmark stress tests didn't crash the card, but the issue in the games persist.

Given that information the only option we have left is a somehow damaged Video Card, the solution would be to fill a RMA, as the card was recently bought. I suggest contacting with the manufacturer instead of Amazon or Nvidia. The manufacturer (if professional enough) would give you a tested card, guaranteed to work, while Amazon will give you another boxed one or a refund if you are a regular client. Nvidia will do nothing they only build the chipset. I've had a reasonably good experience with EVGA for example, not sure about other manufacturers.