Focusing on the 5V rail, Seasonic M12II 520 or (industrial) SS-500 ES gives +5V@24A, but it's not far from the Antec Basic 350 or (industrial) Seasonic SS/SSP 300/350 ST/ET variants (+5V@20A).

Actually I'm quite sure any of these will be enough, unless you're putting GHz+ Athlon with 50W+ power consumption on its own (don't remember which one started into this range). Coppermines and Tualatins are rated 33watts TDP or lower, so you'll be safe there.

The graphics aren't really a threat either, there was a post with estimated numbers on these (probably mine, sourced from somewhere on the net). Though I suggest adding a fan on the Banshee if it didn't have one already -- small passive heatsink is really not enough to keep it cool)

Yeah pretty much any card I will use either has or is modded for active cooling. My Banshee is all decked out with a fan and also ram heat sinks, same as my Kyro II cards.

I had to replace my Banshee under warranty back in 1998 due to artefacts that must be caused by overheating. Met some executive/officer (from Singapore's Creative Tech maybe, though I didn't realize it at the time). I was sitting in the waiting room (at the service center, but I did feel like a patient 🤣), holding the whole box with the Banshee's face and he wanted to take a look at it. 😀

I'd use a quality new power supply. Nothing there is going to be THAT taxing on a 5v rail. The only time +5v becomes an issue is when the board has a special connector for it and you are using a high power cpu.