...if beauty and composure apart from love was what he was after. Jane's beauty and equanimity surpassed Lizzy's. But Darcy preferred Lizzy, IMO beyond "chemistry."

To do my argument full justice, I would have to skip beyond chapter 47, but I will not; but I would say that a man of Darcy's consequence surely has been exposed to beauty before and likely met witty women before. From his description of an accomplished woman in chapter 8 (although some of it may have been included to avoid contradicting Caroline) we know that Darcy has met a few such women without falling (were all "six" already taken?). That is why I think Darcy's fixation on Lizzy is more than lust.

What Darcy presumably thinks he's looking for at Hunsford is a mistress of Pemberley and mother of an heir. What he seems to have found (but has not secured) is someone who may do for him (based on the changes Darcy exhibits at Pemberley) what Charlotte does for Mr. Collins, make him a better person (okay, in Charlotte's case simply hide her husband's flaws as best she can :-).