Is a platform upgrade worthwhile with an RTX 5090?

The answer depends on what is actually limiting you. If your games are already smooth or your workloads are mostly GPU-bound, the platform upgrade may not feel significant. For local AI work, increasing system memory could be more useful than replacing the CPU. Since you’re already finding 64GB restrictive, moving to 96GB or 128GB may help with larger models and multitasking.

A 9800X3D would be faster for gaming, but it has fewer cores and threads than some higher-end productivity-focused options, so it isn’t automatically a better choice for FEA, CAD, or other heavily threaded work. DDR5 can improve memory bandwidth and overall platform performance, but it usually isn’t a dramatic upgrade by itself from a decent DDR4 setup. I’d only switch if you have a specific workload or game that is currently CPU-limited.

You don’t really need to upgrade yet. The 12700K is still a capable gaming and productivity CPU, and the 5090 should perform well with it. A new CPU, motherboard, and DDR5 kit could cost a lot for perhaps a modest improvement in gaming, mainly in frame-time consistency and CPU-limited situations. Waiting for prices or the next platform generation would probably offer better value.

If you decide to upgrade now, prioritize the part that affects your actual workload. More RAM would likely help your AI use more immediately, while a newer X3D processor would mostly benefit CPU-limited gaming. Your current board and processor are still strong enough that there’s no urgent need to replace them just because the graphics card is high-end.