A stable 650 W PSU is fine, you could even go with a 'weaker' power unit. For the 670 and the 970. .
No idea what you mean with good fans on the G1. Are you worried about noise and temperature? Gigabyte is following a very simple solution here. They are using a cooling system with a biger surface and 3 fans instead of the 'normal' 2 fan solution. That makes the card way bigger and a bit more power hungry. Also gigabyte is promising to use only selected Chips for the g1, this gives the card higher OC capabilitys.
But this doesn't make the G1 a quiet card with around 2,6 sone under heavy load. This is still a good value, but not a quiet one. All this combined seems to make the G1 a good card for OC. People are claiming to go up to 1500mhz stable boost with the G1 and still hitting under 80°C. And this is a very good sign.
If you want a more quiet card you could go with the msi or the asus gtx 970.
I hit 1470 with my MSI, it's dead slient, never goes above 65 Celsius.