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.
Option “q” for sure.
When you populate all four slot it is harder to hit high speeds at low latencies in the first place, and with not-identical sticks it’s harder also. I don’t think you can hit even the lower of the values, so 3000 MT/s, with that mix installed.
Even if you could, running only the two fast sticks at 3200 MT/s will help you more for the games. I don’t think you’ll find a situation where a game is not happy with 32 GB of RAM in the system, and could derive any benefit from the additional 16 GB on the older sticks.
Also you neglected to mention any latencies, but they are important to hit too, not just high clock rate. The stick with the highest latencies will be the bottleneck for your memory controller.
(For my comment I’m assuming you mean MT/s not MHz, because everyone keeps treating them as the same, even though they are different by a factor of two. If you actually mean your RAM ran at 3000 MHz so 6000 MT/s then I’m impressed you got that with non-identical sticks, and think it will be even more impossible to hit 6000 MT/s let alone 6400 MT/s with the new ones in the mix)