I posted a thread in the General Forums about using Carl Sagan to finish not only SS projects, but also to build late game wonders and districts each turn for several turns afterward using the overflow production. The exploit is based on stacking bonuses to generate massive production overflow when using Carl Sagan on a SS project. Not sure if it should be banned or not for GOTM, but thought it prudent to share my experience.
In my game, Carl Sagan:
Rushed a Mars project
Completed an Entertainment District (late game)
Built a Stadium (Arena and Zoo purchased turn after District finished)
Rushed The Estadio Do Maracana wonder in a single turn
and continued to generate about 9 Campus Research projects (one each turn) before running out of overflow production
In my game, Carl Sagan:
Rushed a Mars project
Completed an Entertainment District (late game)
Built a Stadium (Arena and Zoo purchased turn after District finished)
Rushed The Estadio Do Maracana wonder in a single turn
and continued to generate about 9 Campus Research projects (one each turn) before running out of overflow production