Phase 5 cards like cv-64/3d with CGX 4 always felt faster than p96 on my A4000-but more of a pain to get working.
The external driver means you install an 3rd party SHAPESHFTER RTG video driver , and then should select this driver.
BUT IMO experience external RTG shapeshifter drivers made very little difference compared shapeshifter's built in RTG driver.
