Let us assume there are 4 slots for RAM in a given motherboard A, B, C and D. Slot A and C form a dual-channel and B and D form another dual channel. (They are of same colour physically.)
Now I have 2 similar RAM sticks of 3000 MHz running in dual channel. I am buying 2 similar RAM sticks of 3200 MHz (only available option for me now)
What would be the best configuration to get most speed in games from these?
p - 2 sticks of 8 GB (3000 MHz)
q - 2 sticks of 16 GB in proper dual channel configuration
r - 2 sticks of 8 GB (3000 MHz) and 2 sticks of 16 GB (3200 MHz) inserted in the 2 dual channel configurations respectively.
I don’t believe “r” is an option, mixing makes and speeds. That said 2x 16 would be better than 2x 8 regardless of speed.
Mismatched capacities do work, all sticks just have to be run using matching clocks and timings, which may or may not be possible. Using the XMP profile of one set may not work with the other, and manually figuring out settings that work with both is not straightforward.
More capacity is not automatically better. As long as your have enough capacity, more speed will net you more performance.
Unless one needs additional capacity, one should go for a faster set over a larger one.