Originally Posted by 5outh
With that PSU, you're 100% fine. I'm trying to find this video I saw a while ago of this guy running dual 570s in a sandy bridge build with an Antec 500w PSU. No luck yet, but I'll post it here when I find it.
650w is enough for pretty much any dual-card setup, and that's a quality power supply. Power won't be an issue.
+1 to this guy.
This is why it's best to ask these power questions in the power supply subforum, rather than the AMD forum you'll get a much stronger consensus of more correct answers (no offense guys, I wub you too).
I'm going to make one last entreaty in this thread, and then I'll let you make up your own mind between dissenting opinions. As I'm assuming you're unlocking your 6950s and overclocking them to at least 6970 clocks, that makes them essentially 6970s (you'll probably bump them up to 6970 volts).
So this review here
measures the maximum
wattage of the entire system at 550Watts. Why is maximum important? Because maximum means peak (the highest spike recorded, most of the time usage is lower), the 650TX is rated for 650Watts of continuous
output, and can peak well above 650Watts.
So, we've already established that your system would be more than fine, but there's a caveat, that 550Watts they recorded? That's power from the wall. In other words, there is an efficiency loss in a power supply when you convert from AC power to DC, so assuming that their power supply was very efficient @ 85%, that 550W wall draw is actually more like 465W of system draw.
And the PSU is rated for 650Watts of continuous
power delivered to the system
So to sum up, 6970s in crossfire running a heavy load, measured to draw 465Watts, leaving >200 Watts of continuous watt delivery headroom on a quality 650W unit like the tx650.
But it's your call of course.