I almost always try and go through STL when flying BOS-DFW as upgrades are very easy. My upgrade percentage has been 100%, and I flew STL-BOS last weekend and was the only one in F (Y was 80%-ish full).

STL-BOS (812) and BOS-STL (1809) gets a dinner service, same as midcons to ORD (no ice cream). Service has always been good.

As a Gold (or even Platinum), BOS-DFW upgrades are difficult. STL presents an "easy" option.

Matt