The most important thing is that the +12V rail(s) has the capacity (amps) to run the card. The GTX 670 requires 173W at max load. That translates into 14.4A on the +12V rail. http://forums.atomicmpc.com.au/index.php?showtopic=264
Unless your 750W PSU is a real cheapie, it should be more than enough. You might want to run the numbers thru a different calculator like this one: http://www.thermaltake.outervision.com/
I don't know how you could have come up with a 900W+ result unless you entered something wrong.
The most important thing is that the +12V rail(s) has the capacity (amps) to run the card. The GTX 670 requires 173W at max load. That translates into 14.4A on the +12V rail. http://forums.atomicmpc.com.au/index.php?showtopic=264
Unless your 750W PSU is a real cheapie, it should be more than enough. You might want to run the numbers thru a different calculator like this one: http://www.thermaltake.outervision.com/
I don't know how you could have come up with a 900W+ result unless you entered something wrong.