Performance (40% of the final score) - Seasonic power supplies have lately been a walk in the park to score, and this will be no exception. This unit's not getting points deducted for voltage regulation, because let's face it... an average of 0.23% in the hot box is still well inside the excellent range. Heck, that's verging on real perfection. No points are coming off for that. In terms of efficiency... again, no points come off. The unit passed Platinum on both hot and cold tests, and it was as clean a pass as I've ever seen. The third of the three main aspects I look at for my performance score is the ripple suppression. Once again, all three main rails were at the 25mV or less mark I require for excellent status there, so no points come off for that. In terms of the other charts and tables, it goes like this: standby efficiency - pass. Low load test - pass. Overshoot transient tests - pass. So, I'm happy to say that the 660XP grabs a 10 here for Seasonic.
Functionality (20% of the final score) - fully modular, no points come off. Adequate connector counts for the power level, no points off. Decent documentation, you guessed it, no points come off. Love the continued presence of a selectable semi-fanless mode. Love the ribbon cabling. Love the sleeving on the ATX cable. Again, we see the varying cable lengths on the peripheral cables for those who could do with shorter cables to assist in cable management. Lots of included goodies. I'm trying to find something to complain about, here, but it's not working. 10.
Value (20% of the final score) - Newegg's carrying this at $149.99 right now. It can be found a bit cheaper elsewhere, but Newegg's price is reasonable compared to some others out there. That said, there are only three units in the 601-700W search bracket that are more expensive than this one. What's cheaper? A whole pile of units, including Seasonic's own X-650. When we go up a bracket to the 701-800W level, we find this unit competing at the same price as the X-750. Finally, moving up to the 801-900W level, we still find some competition to this unit in the likes of the Lepa G850. Granted, the Lepa is unlikely to compete with the extreme stability of this unit, but then again, you're getting almost an extra two hundred watts. All in all, I think the price premium behind the Platinum certification is still a barrier to the value score, here. Yes, this power supply is amazing, but you still do have to presently pay to play at the Platinum platypus party. 8.
Build Quality (20% of the final score) - yeah, there's nothing to complain about here. Seasonic brought their A game to the soldering work this time, and there's nothing about the platform I can criticize. I'd like to see thermal grease added to the 12V output heatsink where the upper part of it attaches, but that's not even necessary, really. I mean, you saw how awesome this unit was in the hot box. 10.
Build Quality: 10Total Score: 9.6