Yorkfield:
 - mmx2: 2.53x (504 vs. 199 cycles)
 - sse2: 3.83x (504 vs. 131 cycles)

Nehalem:
 - mmx2: 2.42x (365 vs. 151 cycles)
 - sse2: 3.56x (365 vs. 103 cycles)

Skylake:
 - mmx2: 1.81x (308 vs. 170 cycles)
 - sse2: 2.84x (308 vs. 108 cycles)
 - avx:  2.93x (308 vs. 105 cycles)