I've experienced some peculiar performance issues.

It's a bit like MSSQL-Gate compared to "Diesel-Gate"

The thing I've experience is that when memory usage increases to > 80% (by other processes) MSSQL starts to consume CPU without even being used. It's looks like it starts to "touch" all its memory blocks to keep it loaded in RAM. This will degrade all other running processes. This behavior will stop as soon as the memory usage gets lower.