Me personally? i love it. Rock solid lines at full system load, and I have yet to see the fan spin for more than 2-3 seconds. Or it might twitch. high efficiency has it's perks. Some of the packaging is unnecessary, but not really a problem.
here's a more professional review,
I know it's expensive, but look at the corsair, against the retail price, it's only $20 more. I know, rebate...but still. Plus, the x-650 is the only modular Gold PSU you can buy right now that's 650W.
edit-the other options are Enermax's Pro-87 and Modu-87 line. These are gold. The pro are non-modular, the modu, obviously modular. check around for availability, they're pretty new, but also very quiet and high high quality. Enermax and Seasonic are the only brands I'd buy.
Your rig wouldn't be on if your 12V rail was at 4.99V. Software voltage reading is practically useless.
However, for a new PSU, and a single card setup, I'd recommend a ~550W+ PSU (because of Fermi's ridiculous power draw).
or if you want modular:
Great quality PSU. No need for a 750W if you're just using a single card.
Edit: Here is a JonnyGuru review for the X650. An amazing PSU.
What other programs read voltages on the powersupply?