If your IPD is 60mm, than 3D objects separated by 60mm will appear at "infinite" depth, so far away that you lose depth perception. You'd only want that for things in the very far distance.
Distance does factor into the discomfort, that's how they're able to get away with much higher divergences in the theaters, because the screen is thirty or forty feet away (or longer, depending on what size your theater is). But, since the eye can only determine depth up to a point, i.e. IPD = both eyes staring directly ahead (not converged at all), divergence of any degree is unnatural. Just because your eyes can do it doesn't mean they should. That's where the headaches can come in. Bottom line is that you never want to push depth beyond your IPD.
Now, as bd2003 said, that's for depth. For pop-out, you can do whatever you want. That's the way our eyes work, they can converge damn near far enough to focus on your own nose. Practically any amount of negative parallax (anything in front of the screen, i.e. "pop-out") is acceptable. But, since we are talking about games here... games tend to render almost everything at positive parallax, for distance and depth, the "window" analogy. That's where you don't want to push too far.
Trine 2 is the only one of the current generation (PC notwithstanding) that I've played, but not lately (I enjoy the look of the game, but I'm rubbish at actually playing it). I seem to recall it had amazing depth but not much pop-out. But on the flip side, I think the effect is adjustable. My recommendation would be to leave your screen settings alone, set the game's 3D effect to put the player characters at screen depth, and just let the game do its thing. The folks that designed the 3D effect in games like that actually know what they're doing.. it's best to just let them do it, rather than think that you can do it "better" (as noted above, this is referring to native 3D and not reprojected 3D).
I learned the most about 3D projection, various techniques of depth and pop-out and so on not by reading, but doing. And the more 3D content I created, the more I learned what works and what doesn't. I've also learned that most people who want to fiddle with 3D to make it "better" tend to not have a clue what they're talking about, and are, simply, doing it all wrong.
Welcome to Rivendell, Mister Anderson.