As long as your motherboard supports Ryzen 5000 processors with or without a BIOS update, I would recommend buying these processors, as potential upgrades. (if improved gaming performance is your only goal)
- Ryzen 5 3600/ 5500 at 5.5 to 6.5k on sale.
- Ryzen 5 5600/5600x at less than 10k on sale.
- Ryzen 7 5700x at 13k around brand new (better gaming performance long term than option 2 since 6 cores CPUs will start bottlecking high end GPUs soon enough, because they have already started to do so)
- 5700x3d as long as it is below 20k new (pay 16k max if used)
For higher performance than option 4 you will need AM5 and complete platform switch which is unnecessary for GPU with 3070 levels of performance.