Use Simcraft for such calculations instead. Training dummies results are not accepted as reliable evidence.
Regarding SCK vs 3 targets, it is a DPS increase.
A great test environment is the roof of the gate between Valley of Honor and The Drag in Orgrimmar. There are 3 boss-level training dummies in range of Spinning Crane Kick.
Even with a whopping 3600 mastery on my gear (which is useless when spamming SCK), it is still a significant DPS increase to SCK instead of our single target rotation. Pretty sure it's in the 25-35% range.
After the patch with our new mastery I'm sure SCK will be even better vs 3 targets.