Found two listings for what is apparently the same item, just sourced from two different places. https://zonegfx.com/pearl-for-genesis-3-8-female/ is sourcing from Renderosity where the creator has moved it to an NLA status...
When you say they're different sizes, are you talking about the overall size of the zip / rar, or the individual file sizes? Reason I'm asking is that a DIM-file (from DAZ) will take up a bit more space than a .rar from Renderosity, due to extra files being included in the archive.
I checked the file size listed on Daz, against the size of the file I have (which is the R3d3rosity version) and they had less than a mb of "listed" size difference. Same content creator, same file name (with the exception of the IM000# for the daz one, vs the RO# for the other), only difference that I would figure is a padding or txt file within the larger file.