In the Wild Card era, NL teams that make the playoffs after a .650 or better September are 12-5 in the NLDS. Your San Francisco Giants just went 19-10 (.655).
This is effectively 11-4 since the 2003 Marlins-Giants matchup was going to produce a winner and a loser no matter which club took the division series.
Of the five series losses by .650 or better teams, three were to the eventual World Series winner and one to the NL champion.
2008: LAD, PHI
2006: SDP* [lost to St.L. WS winners]
2003: CHC, FLA, SFG* [lost to Fla. WS winners]
2002: SFG, STL
2001: STL* [lost to Ari. WS winners]
2000: STL, SFG* [lost to N.Y. NLCS winners]
1999: ARI, ATL* [lost to N.Y.]