Now I'll go ahead on a limb here, but Spartan-IV's have better augmentations than Spartan-III's, but Spartan-III's have more time to get adjusted to it and their bodies are more in "sync" with these augmentations.
Now Spartan-II's are unique in several ways:
Experience Genetically perfect for said augmentations
Spartan-III's are, to put it bluntly, cannonfodder, humanity needed spartans and fast, developing augmentations with a higher chance of succes, allowing them shrug of any failed augmentations as necesary sacrifice.
Spartan-IV's however are made to replace, the ODST's and have almost no failing rate with augmentations. They are just as strong as the other spartans, but lack the experience of a lifetime of war. Now some marines actually didn't actively participate in the ending days of the war, so I can safely say that spartan-IV's are weaker in terms of experience and augmentation than spartan-II's and Spartan-III's.