Make sure you update to the latest Intel driver for the video. I can't speak to the I5, but on my i7 it made a huge difference in frame rates in games. I hover pretty easily at 50+fps in many games.
Thanks a ton for this advice, updating the driver was a bit of a pain (the browser on the device won't even download the zip file) but it was worth it. When panning or rotating the view it's faster now on battery than it was before while plugged in.