Should I upgrade my GPU or move to a new CPU platform for 4K gaming?

The AM5 route makes more sense if you want a long-term platform upgrade, but it won’t transform 4K gaming while you keep the RTX 3080. You’d mainly gain newer platform features, DDR5, and a stronger CPU for high-refresh 1440p gaming. For your stated goal, spend the money on the GPU first and replace the CPU platform later if benchmarks show the 12900K is holding you back.

I’d avoid automatically jumping to the 5080. The RX 9070 XT can be a much better value if you aren’t prioritizing ray tracing or DLSS, and an RTX 5070 Ti is worth considering only when its price is reasonably close to the 9070 XT. The 5080 is powerful, but its price and power requirements make it difficult to recommend purely on value.

I looked at current benchmarks, and the 9070 XT is starting to look especially appealing. In my area, the 5070 Ti costs roughly 50% more and the 5080 is close to twice the price, while the performance gap is nowhere near that large for rasterized games. That makes the 9070 XT seem like a much more sensible upgrade than either Nvidia option.

Upgrade the graphics card first. At 1440p and especially 4K, the GPU is usually the limiting component, and the 12900K is still a very capable gaming CPU. A 5080 paired with your current platform should deliver a much larger real-world improvement than moving to a 9800X3D while keeping the RTX 3080. The main concern is the 3080’s 10GB of VRAM, not that the CPU is suddenly unusable.

Before buying anything, check the games and frame rates you actually want. 4K can be expensive because maintaining high refresh rates requires a very powerful GPU, and the visual improvement over 1440p may not justify the cost for everyone. If your current performance is acceptable, waiting is completely reasonable—there’s no urgent need to replace the 12900K or Z690 system.