According to the Pro Football Reference Game Finder using this query, it is seven for the regular season and playoffs. Three post-merger playoff games surpassed Seattle's five.
The Tennessee Titans defeated the Cleveland Browns on November 19, 2000, by the score of 24 to 10. They committed seven turnovers to Cleveland's one, but thanks to Tennessee having Eddie George and Steve McNair, and Cleveland being, well, Cleveland, they still won the game handily.
Three other teams won the game with seven turnovers; Buffalo defeated NYG with 7 turnovers to the Giants' 2 in 1987, in a 6-3 overtime game involving 6 missed field goals (bet they wish they had Scott Norwood that day). 1983 featured the other two games, with PIT defeating the hapless Tampa Bay Buccaneers with a 7-0 turnover differential, and Miami defeated Kansas City in a turnover-filled game (12 total turnovers, 7 by the victorious Dolphins).
The only three playoff games with more...