2. If I’m stuck at 2400mhz, am I better off with 24GB of slower RAM or 16GB of faster RAM? Gaming is the goal, and perhaps a 5600X is fine at slower speeds and more RAM will be more useful.
This is a very common question through the years, and it's pretty simple to answer.
The faster but lower capacity will be better than the slower but higher capacity until you need an amount the lower capacity can't fulfill. Once a capacity becomes insufficient and starts needing to page heavily, it doesn't matter how fast it is.
So to answer this question, you have to ask yourself the following question; do I need more than 16 GB RAM? If you don't know, you probably don't, but you should try and monitor your RAM needs to confirm it.
But this also comes down to details.
Zen 2 and Zen 3 should reliably do 3,600 MHz (if not then at least 3,200 MHz), probably even with four dual rank DIMMs but not always in that case. This will depend on motherboard, its BIOS, and silicon lottery, but since those later AM4 generations typically do at least that high, then it's more or less "free" performance for them, and you do lose out when running slower RAM due to the Infinity Fabric running lower. I'd consider 3,200 MHz fine for them if you can't reach 3,600 MHz, especially for an X3D, but speeds in the 2xxx MHz range, especially the lower end, would be leaving a lot of performance on the table.
With mixed kits though, you'll possibly have to manually tune settings to get them running at 3,200 MHz together, but it should be possible.
So to summarize...
If I
needed over xx GB RAM, I'd choose the slower option since it's still faster than not enough RAM. If I didn't
need it, I'd consider staying with faster, lower capacity RAM, especially if there's a substantial frequency loss like there is here.
If I was faced with an option that forced me to give up a lot of frequency though, and I
needed more RAM, then I'd probably just buy something that didn't result in either tradeoff.
