For someone like Me Darcy income came entirely from wealth. He wasn't working, and someone in his position wouldn't be. So Elizabeth already knew he was extremely wealthy before seeing Pemberley.
I always took that as implying that what she learned was that Darcy had taste. You can have Darcy's much bruited income as a topic of conversation, no doubt about his wealth, but pounds only buy you so much status.
Hear, hear. And not just taste as evidenced by his possessions, but also the good taste to appreciate her uncle and aunt. I think we should also give some weight to the good impressions that Georgiana and the housekeeper at Pemberly may have made upon her.
Also coincident with her seeing his grounds was here talking there with tenants, servants and relatives who spoke very highly of his character and generosity.
