Linux is pretty efficient with RAM, 8 GB will probably allow you do do most things fine, especially one or two at a time, but 16GB allows for more multitasking, faster ram only gives you a small performance boost in certain niche scenarios.

I'd wager most of the time, 16GB allowing you to keep 2x as much info cached in memory will be a bigger performance boost on average than having a faster clock.

Under your described use case it probably won't make a huge difference unless you're editing massive photos or watching several porn streams at the same time.

I'd stick with 16GB unless you encounter any instability from having mixed spec RAM, at which point I would pull one to see if that solves anything.