I could be wrong, but the way I read it in the Members Forum, you could mix and match since it's all the same family now. Steve Kondris called S4 a "variety pack" for all the V4, A4, G4 and V4 Elite and V4++ morphs.

Use the Stephanie 4 Elite morphs with V4 character morphs if you like or the Aiko 4 morphs... the same goes for clothes and textures. They are all sisters. They probably had to keep the bad armpits so all the V4 stuff would work with it. There will probably be a fix for it here or maybe the V4 armpit fix morph sold here will work with S4E, too.