It'll be comparable in terms of battery life - maybe a bit better since the battery is fresh and your outgoing model is probably hovering around 75-80% health if you use the battery regularly. If you're upgrading, definitely get the 16GB model. You may not notice a difference outright unless you're doing some heavy multitasking, but it's something you will want to have in your pocket over the next three years for sure - and especially when it comes time to sell it long down the road.
To be honest, if your current machine is snappy and still feeling fresh, you can get great performance out of it for the next year or two. The display will be noticeably better in terms of brightness, colors, and contrast, but everything else will likely feel similar to your current model. The new models are considerably lighter, built even better, and as a fan of design I think the feel of the notebook is just as important as the specs, so if you're looking for a fresh notebook with a huge trackpad, tight new keyboard, and bleeding edge manufacturing it's gonna make you happy. If that's minor to you, hold on for another year and re-evaluate.
