The GTX 880M is about as good as a GTX 660. So it'll hold up for future games but not at Ultra settings obviously. Medium-High, you should still be able to pull of 60fps at 1080p in most games.
I's imagine the unlock cores option is more so for overclocking the existing cores and without Advanced Core Control, there really isn't a way to unlock them. The feature has to be built in to the motherboard.