I like
Gwendolen, definitely one of my favorite Welsh names. I like the forms
Gwendoline and
Gwendolyn too (though I prefer the former), and I think
Gwen is a nice NN.
Gustav, on the other hand, is one of my all-time favorites. It reminds me of my love to history (as a
Finn and a history student I've had to learn about the Swedish kings bearing this name) and my grandfather (his MN
Kyösti is a variant of
Gustav).
There are so many great combos in your lists:
Gwendolen Iris and
Gustav Casimir are my favorites today!