This is from the readme file:

What's new in Victoria 4.1?

[ top ]Victoria 4.1 now utilizes ExP technology. Morphs created with the ExP system can be added to existing .cr2 files using a batch file process that updates the current .cr2 file, allowing morphs and morph channels from many different sources to be added in without overwriting each other. (Morph channels allow INJectable morphs to be used, keeping the morph information outside the .cr2 until INJected into the figure, to keep the file size down.) Please see the ExP FAQ for more information.

Note: Due to the way Poser reads the ExP files, it is strongly recommended that Victoria 4.1 be kept in the default Poser Runtime. DAZ|Studio users can place Victoria 4.1 in an external folder if desired.

A new, sample resolution map with a bikini has been provided.

The upper and lower jaws can now be moved independently.

Visemes have been added for better speech representation.

I think that the only compelling reason for getting V4.1, for those who want to use V4, is that new material will almost invariably be based on V4.1, not on the original V4.   She looks the same, apart from the daft bikini and the Guantanamo haircut.   I've always had a bit of a problem with the manic stare that V4 comes with (pretty much on a par with that of the Mk.I Jessi), but that's still built in to V4.1.

4.1 also adds an eyebrow "prop" for transmapped eyebrows, but I'm not sure if any characters currently available use that approach.

Some do, I think, as I have seen the odd product that emphasizes that difference.