I'm not an expert on the subject but I think it's a bit of a balancing act - undervolting reduces the power to the chip so it produces less heat and can sometimes be more efficient as a result. But if you go too far, it won't have sufficient cpu/gpu power and the framerate will suffer. Overclocking works in the other direction.
I've actually been looking into this myself, and Kobo seems like the most 'open' option. The Libra 2 in particular fit my requirements for size and features. It supports quite a few ebook formats but I think it's limited to Kobo's own audiobooks only.
If anyone has one I'd be interested to hear your thoughts.
I'm not an expert on the subject but I think it's a bit of a balancing act - undervolting reduces the power to the chip so it produces less heat and can sometimes be more efficient as a result. But if you go too far, it won't have sufficient cpu/gpu power and the framerate will suffer. Overclocking works in the other direction.