I wrote a code to test, which way is faster. I run the code in Release x64. I have VS 2015 Pro with .NET Framework 4.6.
#if SYSTEMMATHLIB using System.Numeri
I decompiled System.Numerics.Vector and I realized, SIMD is implemented only for Vectors and not for Matrix4x4. So Hans Passant was right.
I hope they will also add support for SIMD Matrix soon.