To the OP: I also have a 6D and like many others on the form, I think getting a 24-105L is an excellent idea. You say you want to figure out which focal lengths to get, well this lens plus EXIF information will allow you to do just that. It's also a great lens on the 6D. You might be amazed at what this lens can do on the 6D. (OK, maybe this lens is not as outstanding as the 24–70 2.8 II, but it's great nevertheless.) And, while I don't know this for sure, I would think it would be easier to resell a gently used 24-105L than it would be to resell some of the vintage glass you are considering buying. As I said, I don't know this for sure, but it is something to consider and check out. And think about the total cost of these lenses, which includes the net cost of buying and reselling them and the adapters. In particular, be careful not to overestimate how much money you can get from reselling any of these items. But, if you really want primes to use, here are the focal lengths of the lenses I owned when I had a film SLR: 28, 55, 105, and 200. This set of lenses served me quite well, although once I experienced what modern lenses could do, I sold them. In your own case, since you already have the 50, you could get a 24 or 28, and then get a prime (or as we used to call them in the older days, a fixed focal length lens) anywhere between 100 and 135.