While Peralta’s surface numbers on four days rest were better this year (a 2.59 ERA compared to 2.65 on five days’), everything else indicates he actually pitched much better with greater rest. In 17 starts with exactly five days between outings, he owned a 0.982 WHIP and 3.41 strikeout-to-walk ratio; in the four times he went after six days or more off, he had a 0.851 WHIP and 4.17 K-to-BB.
Plus, saving Peralta for a potential Game 5 would also mean he could pitch Game 1 of the National League Championship Series should the Brewers win at Wrigley in Game 4.