Reminder: The Guts Formula
Y axis is stamina drain multiplier in the late phase.
X axis is guts

80 = 1.9x.
105 = 1.8x
185 = 1.6x
265 = 1.5x
420 = 1.4x
740 = 1.3x
1666 = 1.2x - possible in the future.
6666 = 1.1x - pretty sure this isn't possible