I tried march=native, it didn't do any better than just using SSE2 for me.
Specifying all the SSEs as well as AVX (I was using a 2600k) made a big difference.
You seem to have misunderstood the thread. It's about Amazon EC2 computing. I.e rented computers, not a personal computer.
If march=native doesn't detect high level SSEs and/or AVX, it doesn't detect it.
Doesn't matter what the computer is being used for.