Thanks for all the nice comments! Duncan may be part gordon setter. I adopted him from the SPCA and they had him listed as a gordon setter mix. The only similiarity really though is the coloring and the lean body.
I was also going to ask if he was a gordon setter mix. I think this is the first time I've seen any larger/clear pics of him! He is just gorgeous! Jack and Morgan are cuties too! What mix is Morgan?

We had a gordon setter at work once, and he was H U G E !!! I'm sure they all probably don't get that big, but he was monster-sized lol. Pretty boy.