I would say the 1.7 times larger is about right. I have both Rouens and White Golden Hybrids from Metzer Farms. The WGH's give me an egg a day and have been for about 3 months now. The Rouens have been laying for about 2 months and one has been hit or miss.
I have converted a few folks to duck eggs since they have a richer flaver and larger yolk. The fans who like fried eggs will become loyal converts. And as stated earlier makes for richer baked goods.
The biggest problem is wanting to eat more because they taste so good.
Mond you, I have both ducks and chickes so I compare the flavers and qualities side by side regularly.