The EVGA SuperNOVA 1000 P6 is a good product, which has some room for improvement. The 5VSB rail's performance is not on par with the performance of the rest circuits, and this has to be addressed the sooner the possible. It is a shame to have a Platinum-rated power supply with low efficiency at 5VSB.
Moreover, the fan speed profile could be more relaxed, given that the average noise output is higher than the less efficient, 1000 G6. On the other hand, the PSU's build quality is high, and the average performance is also increased thanks to the excellent ripple suppression, the tight load regulation, the good transient response, and the long hold-up time.
Given that the 1000 P6 doesn't offer notably more than the 1000 G6, you can go with the latter and save a notable amount of money if you don't care about a 2% difference in overall performance. If you want the lowest possible noise output, the best PSUs in this regard are the Asus Rog Thor 1000 and the similar-capacity SilverStone Strider Platinum. The 1000 G6 is also less noisy than the P6, registering 4 dBA lower average noise output.
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Disclaimer: Aris Mpitziopoulos is Tom's Hardware's PSU reviewer. He is also the Chief Testing Engineer of Cybenetics and developed the Cybenetics certification methodologies apart from his role on Tom's Hardware. Neither Tom's Hardware nor its parent company, Future PLC, are financially involved with Cybenetics. Aris does not perform the actual certifications for Cybenetics.