7800-X Average FPS 171 (100%) 4.6Ghz (100%)
2600 Average FPS 168 (98%) 4.2Ghz (91%)
So with 9% higher clock the 7800X is 2% faster, a difference of about 7% IPC to the 2600.
Yes its give and take some in this review and this is an accumulative result however there are a lot of games in it that are traditionally Intel heavy, or at least they used to be vs Ryzen 1###.
For example:
Farcry Primal
GTA-V
PUBG
World of Tanks
Ryzen 2### vs Coffeelake
8700K all core boost 4.3Ghz, single core boost 4.7Ghz
MT
2600X @ 4.1Ghz (100%) score 1439 (100%)
8700K @ 4.3Ghz (105%) score 1419 (98%)
At 105% clock speed vs Ryzen 2### the 8700K scores 98%, a difference of +7% IPC to Ryzen 2###
ST
2600X @ 4.1Ghz (100%) score 176 (100%)
8700K @ 4.7Ghz (115%) score 198 (113%)
At 115% clock speed vs Ryzen 2### the 8700K scores 113%, a difference of 2% IPC to Ryzen 2###
@Martini1991 the numbers say Ryzen 2### gained 10% IPC, that's in line with what AMD said.
Edit: 159 at 3.9Ghz / 3066 ST