Always go a bit more than what you need I always say. If you are keeping something for 10 years and can afford it, go for it.
With an 80 plus platinum PSU it is going to be 90% efficient at 20% load, 92% at 50% load and 89% at 100% load. So if you are going 1200w, and your rig draws 600w when pushed/gaming - you're in the sweet spot. My GPU has been reviewed drawing 391w when gaming, call it 400w for ease. Imagine running on an 850w PSU. Half that capactity has now gone just to the GPU when gaming. How much does a 9800X3D use. Is it 120w? So we're at a potential ~520w and haven't included other bits and bobs from a rig sucking the juice. A 50% load in this example, would ideally need a 1000w psu, for peak efficiency. I just personally don't like the idea of running near or at full load (even though you can). Your just gonna be generating unneccesary heat, noise and waste energy. If it isn't a platinum rated PSU, say gold, the efficiency is 2-3% less. For an 850w PSU you are wasting about 110w. I think I'm right in saying that. Someone will no doubt call me out lol.
Thanks.