Yorkfield:
 - mmx2: 2.45x (279 vs. 114 cycles)
 - sse2: 3.36x (279 vs.  83 cycles)

Nehalem:
 - mmx2: 2.10x (192 vs.  92 cycles)
 - sse2: 2.84x (192 vs.  68 cycles)

Skylake:
 - mmx2: 1.75x (170 vs.  97 cycles)
 - sse2: 2.47x (170 vs.  69 cycles)
 - avx:  2.47x (170 vs.  69 cycles)