That's pretty good - anything around 25-27db under load is not bad at all
The 570 should be more similar to the 580 than to the 560, so I think if in case 28-29dB should be more probable than a 25dB mark.
Afterburner may help to game a bit more quietly, but take also note than currently most of 570s goes in the 31-37dB range at peak load, a really uncomfortable level.
I had the 580 TF that I returned for some crashing issues. Apparently on the MSI forums, there is a BIOS update that resolves that and also allows a lower minimum fan speed setting. At the previous minimum fan setting, the Frozr was certainly quieter than reference 580 or 6970 cards I tried at idle. It was still clearly audible and the loudest thing in my case, though. With a reduction in the minimum, I suspect it will be barely audible in a good case that doesn't have vents at head level. At a gaming load, it will still ramp up to a modest volume.
The card I have now, the Asus 580 Direct CU, is louder at idle. On the plus side, I can keep it manually at the minimum fan speed and the temps don't go beyond the mid 60s, even with the worst gaming load I tried on either card (admittedly not a really intensive game). That's about 10C cooler than the Twin Frozr, even allowing it to ramp up to higher RPMs on a fan profile.