Clayton Kershaw is on pace for 11.3 WAR this season, which, as measured by WAR, would be the second-best season any pitcher has had since 1920 (behind '99 Pedro Martinez). For older WNFFers, he's on pace to be 1972 Steve Carlton. Since 1920, there have only been seven 10 WAR pitcher seasons.
Old school stats now: Kershaw is also on pace for 245 innings, 290-300 strikeouts, a sub-1.75 ERA and 22 wins. (Note he's thrown 20 more innings than Arrieta.)
Since 2000, the only guys with 300 strikeouts in a season are Randy Johnson, Curt Schilling, and 2015 Clayton Kershaw.