That's definitely tops. The next best would most likely be Hack Wilson from 1927-1930, when he posted a 1.051 OPS. His overall numbers in six years as a Cub are great with a line of .322/.412/.590 and an average of 31 HR, 108 R, and 128 RBI per season. Hack is problematic because his astronomical numbers were in large part due to the crazy offensive era in which he played. The ridiculous offensive numbers of the late 20's-early 30's stand as the only real rival to the steroid era as far as offensive production. Consider that in Hack's best year, 1930, the LEAGUE batting average was .303. Thus, one could (if they wanted to) quite convincingly dismiss Sosa (roids) and Hack (softball league stats) from their lists of greatest Cubs hitters. If one were to do that, I'd think the clear remaining choice is Billy Williams. Completely contrary to Hack, Billy put up the bulk of his numbers while playing during an era dominated by pitching. For example, take 1963 and see that the league BA was just .249. You have to go back to 1917 to find a league BA that low. So for Billy to hit a career .290 during an 18 year career when the league average was .254 over that same span is pretty impressive. His 133 career OPS+ over 18 seasons is pretty damn nice as well. I guess I've convinced myself in doing this research right now. I'm gonna go with Billy Williams. final answer. The thing is though, Wilson's OPS+ for his six years as a Cub was 155. Billy Williams' best six-year run was 141. Sosa's best six-year run was 162. So while Sosa and Wilson may have played in better offensive eras, their numbers are still better relative to their respective leagues. This certainly isn't a knock on Williams, who was a fantastic hitter. Isn't OPS+ adjusted for the league/era in which you played?