Silicon lottery.
Also I guess scan algorithm is kind of "safe", so it would not give you best possible result. Also I tested that evga OC scan, asus gpu tweak scan and MSI afterburner OC scan gives the same result, so this scanners all similar and maybe it is just nvidia OC scanner with different skin :)
 
As for me - my results kind of similar: +75-+80 or something like that.
I tried to go further and reached +135 - I can pass 3dmark timespy benchmark, but it would crash often. +120 - 3dmark works fine, but sometimes it crashes in games. +105 - seems perfect for games except r6s: I was getting "gpu hung" r6s sometimes. So +90 is my result I guess. But for beautiful numbers I can set it to +100: it seems that actual clock settings must be part of 15mhz, so you should get nothing if you set +10mhz or +5mhz.

Hello My result is +141 score and memory oc 1000
Good ship or normal
 

Asryan
Can't go above +100

Silicon lottery.
 
Next topic.

bdary
One thing to keep in mind looking at various core overclock numbers is that the FTW models ship stock with higher clock speeds.  So where your GPU maxes out with a +100, could translate to a +130 on a lower model card as an example.  You can't simply go by the amount of the offset, but rather what the card frequency actually runs at.

+1  This.