Yes, 4th gen are better than corresponding 3rd gens.
But, here, the comparison is in between a 3rd gen i5 M-series & a 4th gen i5 U-series.
i5 4200U is clocked at 1.6 GHz (upto 2.6 GHz Turbo)
i5 3230M is clocked at 2.6 GHz (upto 3.2 GHz Turbo)
You can see the performance list here, base on...