I had mentioned before (when talking about the thermally improved layout) that in addition to the improved layout, I'd make the production #LiFePO4wered/USB base boards with 2 oz copper, and that this hopefully would improve thermal performance even more. So meanwhile I have been able to run some tests on production boards, and it sure does:

The graphs show the battery voltage when charging from empty loaded with a Pi 3, connected by Ethernet and with an SSH connection for logging. As you can see, the 2 oz copper presents a significant improvement.

It also looks like the heat sink doesn't make very much of a difference. Because of this, I'm going to provide the heat sink as an option instead of building every #LiFePO4wered/Pi with a heat sink attached. All the pre-release units will continue to be shipped with this option though.