while falling ~3% behind in games clock for clock
I'm not lazy to check the numbers, and here they are for 6/12 CPUs, directly from the link:
Ashes of the Singularity
2600X still a whopping 11% slower than the 8700K
Assassin's Creed Origins, ultra quality
8700K is a further 14% faster [than 2600X]
Assassin's Creed Origins, high quality
8700K is 12% faster than the 2600X
Battlefield 1, ultra quality
2600X is still 7% slower than the 8700K
Battlefield 1, medium quality
2600X now 10% slower than the 8700K
Far Cry 5
2600X is still 8% slower than the 8700K
Italic font is used for quotation here.
Now that we see the picture in gaming with 1080Ti GPU, we can say, that AMD needs 10-15% IPC increase to be on par with the Intel 6/12 part. Given that Intel CPUs have higher boost clocks, it's not unusual that the audience like to see this margin could have been finally covered.
Verdict:
10-20% is what users actually want to get from Zen 2 because it's the actual margin in gaming. That's why when we talk on forums we mean these numbers, and when we see them we feel it's close to what is just expected from AMD to catch up with Intel.