Actually, Microsoft does test these scenarios, but they test them with their own components. It is up to the driver vendors to test their drivers (as part of the WHQL logo process) to validate that they don't break the process. When Windows bugchecks, it does so because something bad happened, and Windows (or a driver) calls the KeBugCheck routines to shut down the machine to avoid potential hardware failure and/or data loss. The fact that you have bugcheck codes that are all over the spectrum, and driver verifier has found issues multiple times would indicate either you have one of the most unlucky installations of Windows, or you have hardware issues.
An easy way to test if this is hardware or software would be to install STOCK WINDOWS without any drivers other than what installs during setup (offline, so as to not pull anything from Windows Update either), and then stress test the system. If it still fails under heavy load, you have hardware issues. If things work, add drivers and retest - if things fail then, it's drivers. If things still pass, add software and keep retesting until either everything fails, or you are stable. At this point, you're simply blaming precisely because you cannot figure out why things keep failing. I empathize with you here, of course, but you have to understand that Windows is not recompiled every time it is installed, and there are literally hundreds of millions of installations out there that are not behaving the way you are experiencing it. At some point you have to agree that the most logical conclusion should also be the correct one - either everyone with Windows installed would be running into these same issues (and Microsoft would be fixing them post haste), or there's something special about your install. Since the Windows codebase would not be the special part, work forwards - drivers, software, or hardware would be potentially different from other users, and thus the likelihood is that's where the problem lies. It's always possible, however minute the chance may be, that there's a Windows bug you're triggering that throws all these different bugchecks and driver failures. It's just not likely.