Rather than answer all of the above questions, let me try to put you out of your misery...
The one piece of the puzzle you're missing (and others haven't pointed out) is that...
Since SPCR's claim is true...
...is true, for each given level of input heat
. Transfering heat from one source and/or medium to another (via convection?) is largely governed by the difference in temperatures between any two sources in the pipeline:
cpu->IHS->TIM->HSF baseplate->heatpipes->fins->fan-fed case air->room air
...be sure not to gloss over this:
What this tells us is that for this combination of CPU, load, and heatsink, the airflow of an 1100 RPM 120mm fan matches the rate of thermal conduction from CPU to heatsink fins.
...if you generate more heat at the cpu level (using the same HSF), you're either going to have to move the air across the fins faster or lower the temperature of that ambient air.
So, SPCR does thier tests with X amount of input heat being generated (they're not interested in results of other heat levels, according to a post on the first page of this thread). What they are saying is that for X amount of heat, with a similar ambient air temp, using a similar case and/or airflow configuration, you reach the point of diminishing returns above ~1200 rpm on a Ninja.
Note that 1200rpm is not some magic number for the Ninja in the general sense. Thier results do not say anything about a CPU putting out twice as much heat, or a situation with higher ambient temps, or one with a more constricted airflow. Each of those conditions would have a higher "rpm point of diminishing returns".
This explains why AnandTech is getting more cooling with faster fans, when SPCR didn't see the same effect - they're testing two different configurations.
Having said the above, that 1200rpm figure for the Ninja (under the SPCR test conditions) may or may not be the right number for the Tuniq Tower, Ultra 120 or any other heatsink. I believe that the general conclusion that SPCR reviews have come to is that the Ninja gives the best amount of cooling, for that speed (generally related to noise level) fans. A Tuniq or Ultra 120 might require a faster fan (because of tighter fin spacing) to cool as well as the Ninja (again, at the tested configuration).
The flip-side of that coin is that that "point of diminishing returns" on fan speed is reached earlier on the Ninja than the heatsinks with more tightly spaced fins (all other factors being equal).
In short, while what they are saying may well be true - for thier test configuration - it can't be applied "literally" to other configurations - it's just one data point.