You even have hardware intrinsics available to play with, and for performance-sensitive libraries such as hashing algorithms, it's typical for performance to come within spitting difference of RAM speed.
Where on Earth? I could tell you precisely where if it mattered. I'm certainly glad the team at MS has been focusing on performance now because they certainly didn't when the team I was on decided to try it. (Hey, maybe they could help out the Visual Studio team as it takes like 10-15 seconds to open the app to an empty screen).
I haven't run any tests lately (and probably never will as I'm not interested in a language that emits IL rather than machine code; or a language that uses a GC) so I apologize for throwing out the 15x number when it is probably not correct. It won't happen again.
I would wonder why some game studios (like Supergiant Games / Hades) ended up porting their C# game engine to C this year? Was it because C# was fast enough? Or maybe it was to make the game more portable to other platforms? Not sure.