Really posh people have solid, traditional names, plus outlandish nn.
For less used names, how about:
Araminta, Eugenie, Iphegenia, Artemis, Juno, Berengaria, Edwina, Georgiana, Clelia, Wilhemina?
Clovis, Rollo, Florian, Caspian, Marmaduke, Christian, Jeremiah, Kenelm, Neville, Orlando, Percival, Warwick?