For defense against people in the woods, you don't need anything more than a 9mm. Period. You don't have to factor in shooting through barriers, like auto glass, or doors. You will be face-to-face with an unarmored target. Any barriers out there would likely stop any other round as well (tree trunks). The weight savings and added capacity will seriously outweigh the diameter of the bullet, not to mention the easier follow-up shots.
If you were talking about hunting hogs in the woods, I would probably suggest a Glock 20, so you can take advantage of the added benefits of a full-powered 10mm round. For people, the rounds just don't do any better than each other. I have worked with trauma gunshot victims routinely for the past few years, and you would be hard-pressed to find anyone in the field who can attribute anything of significance to the caliber of your service pistol.