I'm running 20x8.5 with 255/35/20 and 20x10 with 275/35/20. What's the correct tire pressure?

 

35psi.
read the Door Jamb. Really does not matter what size tires as the car was developed for tires at the pressure stated on the Jamb.
Racing , etc...etc..may use different pressures , but for street driving....35psi.

 

My door sticker says 32 psi for 235/55R17 tires.

 

For the low profile tire you have, for street you might consider higher pressures. Remember the section height is much shorter so the tire has less deflection capacity before you pinch it on the rim. My Volvo with 45 series takes 38 psi with full vehicle load and that ain't enough.