Depends on how long you are going to keep that PSU and how much power you’re working with, and the climate you’re in.
More to my point: It gets fucking hot in my room in summer with the comp running, even in a mild climate, and I don’t want the computer shooting out 5% more heat and making it more uncomfortable

Depends on your price per kilowatt hour.

A PC pulling 300w with a 600w bronze PSU (~85% efficient) will be pulling ~350w from the wall. With a gold PSU (~90% efficient) will be pulling ~330w from the wall.

So, for every hour of playing, you’re saving 20 watt hours. Thats 50 hours of playing to save a single kWh. Assuming a 25 hr gaming week for a moderate player (full time job, gaming after work and on weekends), that would save you 26 kWh a year.

Depending on your energy costs, and how you expect them to change in the future (almost always going to go up), you can probably expect the PSU upgrade to pay for itself in ~3-5 years if you have a moderately high cost per kWh (like 30 cents or more?).

High efficiency PSUs are gonna pay for themselves faster the more you use them. If it’s a one time thing for someone that’s only going to play 2 hrs a day, bronze is probably the better option (but you still want a quality bronze one from a known good manufacturer). If you’re gonna move your PSU in between builds it’s more of a decade long purchase and will continue to save you in the long run. It all just depends on the situation.

If you’re just building this for a colleague that doesn’t play much, give them a quality bronze PSU and (and maybe upgrade it if you can find a quality gold for another $10-15).