The Porsche suspension spec ranges are:
Front camber: -.7 to +.3 deg.
Caster: 7.5 to 8.5 deg. (not independent; changes with other settings)
Front Toe: .00 to .08 deg. each side; total toe .00 to .17.
Rear camber: -1.8 to -.8 deg.
Rear Toe: .00 to .17 deg. each side; total toe .00 to .33

To reduce understeer, increase front tire pressures by 3 or 4#, set front toe near zero, camber near -1 degree, and/or slow down.