680 7970 is a personal preference. Get whichever you like. I personally like the Nvidia GPUs but with the latest drivers AMD became a better purchase price/performance wise.
About the fans, you can replace them with Noctua 40mm fans. Look back few pages and you will see people using quieter fans.
Also you can always take them out OR you can go to Asus Suite 2 and make a USER profile and EDIT the profile in a way that the fan will spin 40% IF the temperature goes to 70 degrees or something like that. I personally have the asist fan settings to FAN OFF. It does not turn off the fan but makes it work only at a certain higher temperature
But again if you want them to be off, just unplug them
Anyway, the fans have been a major discussion point for a long time, so search the thread and there are numerous postings regarding them. To the OP, I also gave step by step instructions pretty much to how to set the profiles for the quietest fan options. Not sure how many pages back, but was just a couple weeks ago.
Depending on your overall components, the fans may or may not be noticeable. I keep my rig on the ground and run 6 case fans on top of my h100 cooler, so those 40mm I can't even hear... As far as disabling, just go into bios and in advanced mode toward the bottom you should see the option for "asst 1/2 fan" controls or something to that effect. The 40mm fans your referring to run on the asst 1 and asst 2, and if you have them connected, can't be fully disabled to my knowledge. However, you have a couple options to minimize noise.
First, if you enable the Q-fan control, you can then either set them to "silent" or "fan-off." Silent basically auto adjusts to run at lowest speeds depending on temps, and "fan-off" completely turns them off when mobo is idle or decreased past a certain temp.
If you disable the q-fan control (out of box this is disabled), and your asst1/2 profile is set to manual, then you can adjust the upper temps to a higher setting so that it takes a hotter temp to cause them to run at max speeds.
Also, by setting the lower temps at a higher degree, then it will cause the fans to run at minimum speeds at a higher threshhold.
From here, just mess with your min/max duty cycles (i think min is 60%) to get the slowest speeds.
Edited by likethegun - 11/15/12 at 5:18am