I get the same battery life in either tablet or laptop. If your primary reason is drawing in landscape you can flip the screen on the Surface Book and leave it attached.How is the sp4 more flexible? Fridays coming and I feel on the fence now. It's the screen and drawing space that has me hooked. Being able to surf like a laptop on the couch makes a big difference for me too. I love my sp2, screen space is the only complaint
Depending on your tools (Adobe CC, Magna Studio, etc.) you may find scaling issues, at least CC has a "Surface Mode".
With your use case the Surface Book may work better but you will be pushing many pixels with the same GPU I use.