My trusty 40D is now 7 years old. It has and continues to give me good results when I do my part.
It's a great camera with my EF-S 17-55mm f/2.8 IS lens.
I recently bought a 24-105mm f/4 L lens. So far, love it!
I was advised before I bought the lens that it wasn't made for a crop camera and was much better on a FF body, I knew that going in and don't regret the purchase.
After reading all I can on the use of this lens on the 40D vs the 6D, I'm thinking it is time for and upgrade to FF. 
I only have three lenses that will work on the 6D but for now I think I can get by with those.
Canon EF 70-200mm f/4 IS
Canon EF 24-105mm f/4 IS
Canon EF 40mm Pancake.
My concern is, I don't think I'm really that good of a photographer to warrant the extra cost to transition to FF.



