Two 12V rails?

Newbie here, so I apologize for any misposting on my part.

Recently upgraded to the new nvidia geforce gtx 580 processor, which requires 600W or greater with "a minimum of 42 amps on the +12V rail" to quote the specs.

Now, I have a nzxt pp-600 psu, which is 600W and has two +12V rails, the first with a max amperage of 21A, the other 22A.

So before I run out to get a new psu, I just wanted to confirm that this won't be enough... shouldn't I theoretically be able to get 43A from this setup if I connect the gpu to both rails? Of course, minus the current taken by the case fans...

a power supply is never really going to put out it's full rated wattage

it may be labeled as 600, but it's max output will probably be around 580 or so.

you always want to overshoot the total wattage you'll need. this keeps the power supply from being overworked, and keeps it running a lot cooler, and extends it's life

if the card alone is saying you need at least a 600 watt PSU, you'd be best off adding another 100-150 more than that for everything else, and shooting for a 700-750 watt rated PSU, and then you'll know without a doubt that you'll be set

you could probably run your current PSU temporarily, but I wouldn't run any games that require high GPU usage. as soon as that GPU comes to life and needing power, the PSU isn't going to be able to keep up, and the computer will probably become unstable and crash. the crash may be harmless and just require a reboot, or it could cause things like HD faults and may actually mess up some system files. so your best bet would be to not run it until you upgraded the PSU