Although you wouldn't know it from the documentation, both the GK10X/GK11X silicon had serious problems with the global memory barrier instruction that had to be fixed in software after launch. All global memory barriers had to be implemented entirely as patched routines, several thousand times slower than the underlying, broken silicon. Amusingly, that same hardware defect forced the L1 cache to be turned off on the first two keplers. I suspect if you ran the same benchmark on GK110 and vs the GK210 used in the article, you'd be surprised to see no effect from the L1 cache at all.