Even if you never hit the 8gb ceiling, having some room is not bad. That's because how operating systems work. The less free RAM you have, the more of the RAM are parked outside into files, for parts of the RAM the system and applications thinks it is not crucial to the performance and not used in a while. Emulating 16 bit games won't require much RAM. Editing images will require lot of RAM and benefits from fast RAM the most (out of the activities you described). Browsers require lot of RAM too, but does not need fast RAM.

Without any benchmarks and real world testing, overall in doubt, 16gb is a better choice than 8gb on modern operating systems and activities, unless you know for a fact that the 8gb are not limiting and you benefit from the speed bump in very certain applications. If you can, why not remove the additional 8gb to have consistent set with higher clock speeds and test it yourself for a day or so and see how it works out?