Less power get better performance ¡?¿!

[Shonumi]

Sandy Bridge was notably faster than Nehalem for Dolphin when it came out (10~15%? I dunno, that was before I joined) and Haswell is 25~30% faster in Dolphin than Sandy Bridge. So it's actually not surprising that the i5 Haswell outperforms your older one. Intel has done a lot of work over the past few years to increase their single-threaded IPC.