I have both the 6D and the pancake. The IQ is really great for the price and as you said, the size and weight advantage is obvious. It can make the difference between taking your 6D with you or leaving it at home in certain circumstances. I don't have many pictures worth posting as I didn't have many occasions to take pictures with this combo lately. If I get something in the near future, I'll post it here.
I can't be too specific because I don't have any 35 or 50 to compare the pancake to, but if you're not planning to buy the sigma soon and considering the price of the pancake, it would be a great way to wait for it. I think that even after buying the sigma, you could find a use for the 40mm with its unique advantages.