I have an 03 with 18s. I run 36 rear and 31 front. There are a lot a variables to tire pressure such as driving style, personal taste, and even tire brand and compound. I've found on my car that if I raise the fronts a couple of pounds it will take some of the understeer out of the car. I've experimented with pressures in AX and this seems to work the best for my likes and my car.
Dave - 06 987 S coupe SG/NL; gone (but still my first love): 03 986 AS/GG/BK;