Take most reviews noise levels as a very rough guide on what cards are loudest etc. For example the sound levels you linked to show the R9 290X at 54db at load. An earlier review from the same site shows the same card at 42.5db. Most review sites use open case systems and they place the microphone very close to the actual cards. This is not indicative of a closed system at all to be honest.
The fact that the same site shows the same GPU (290X reference) at vastly differing noise levels shows they are not consistent in their testing methods. Or they have significantly changed them at some point.
http://hexus.net/tech/reviews/graphics/70913-sapphire-radeon-r9-290x-vapor-x-4gb/?page=10
Another thing to consider is that the 71c load temp allows you to use far less aggressive fan profiles than a reference 980Ti. This will reduce noise levels significantly just by allowing the GPU to run 5-9c hotter. Even then it will still run cooler than a reference 980Ti.
980Ti AMP! = 71c load
980Ti reference = 83c load
Here is the EVGA ACX 2.0+ 980Ti review from the same site. It is quieter but runs 5c hotter at 76c, allow the 980Ti AMP! to run at similar temps would give similar noise levels IMHO.
http://hexus.net/tech/reviews/graphics/83819-evga-geforce-gtx-980-ti-superclocked-acx-20/?page=10