It's not so much the drives as the maximum the CPU and GPU can/will pull. A modern GPU can pull 200-400 watts on it's own under full load.
I don't think i've gone under 500watts for a PSU in any build for 20+ years, and I'm running an 800 or 1000watt one at the moment (I can't remember the model), because whilst I know I'm not going to use that much it allows some headroom, and most PSU's are happier running at below maximum output as much as possible.
Remember modern PSU's basically only draw as much as you are actually needing as long as it's below their rated output.
Yes, but he said he's not having a discrete GPU, and only a 65w TDP CPU, 600W is massive overkill for that