I dunno. I know that a Spartan IV can't wear a SII suit because the SIIs have augumentations on a whole nother level, ceramic bones and such. And I know the suits the IVs wear are made to make up for the lesser augmentations with greater increases in response times etc.
I'm not sure why Spartan IIs haven't gotten the most advanced suits yet then. Maybe just because ONI wants their spartan IVs to be the best, where IIs are more loyal to the UNSC?
Heck, a spartan II in a spartan IV suit probably wouldn't be used to their full potential even though the suit is better, because it isn't taking into account their extra augmentations.
I'm curious if Locke just has a spartan IV suit, or if it's extra special with Spartan-hunting capabilities.