Right now I have a 3.33 Ghz 661 i5 processor. When I do upgrade it will be a new build minus the HDD's. Swift 810 and WC. I could always get the 8150 and upgrade to the piledriver after the prices come down a bit after launch.
Overclock that i5 to 4.0Ghz+ and wait for Piledriver.
You would be cutting it close... how many fans and other HDD, and also the age of the psu you are running will make a difference too.
Plug your details in here for a ballpark: http://www.thermaltake.outervision.com/
Well that ain't good. I just ordered an XFX 7970 3 GB......
Will I be ok or are you saying it won't operate well?
with an overclock on the fx, your looking at 400watts or so at 4.6 ghz or so. 4.6+ is where you really start to add in the watts. With a 7970 in the loop that is another 300 watts. If anything you can just not overclock your processor as much with a 620 watt power supply.
For some reference i run a 850 watt power supply. With my Fx at 4.9ghz (1.45 volts), and two gigabyte 7870's in crossfire. Draw at the wall is around 700 watts fully loaded.