General performance is up ~5-10% from benchmarks ran on other computers.
Battery life stays the same.
It's a very minor boost there. The update to Kaby Lake would be almost pointless except, maybe, that it might provide a good boost to >4K content playback (which will help with Final Cut Pro as well) since Intel is upgrading the built-in video accelerator.
So if you are a heavy iMovie/FCP user, you may see some improvement.
Otherwise, finding a 2016 model at a discount would be better.