Will bigger rims and lowered suspension effect PSM???

[ChrisZang]

I think you will be facing a multitude of issues PSM being the least of all:
The first problem will be ABS, I believe the new diameter must be within 3% of the old diameter, here is an online calculator: http://www.discounttire.com/dtcs/infoTireMath.dos I'd guess that the same rule of thumb will hold true for PSM

The next problem you will have somewhere I have read that 986 are officially only designed for 16" ~ 18" rims.
The larger the rim, the lower (stiffer) the sidewall and the suspension will have to absorb more bumps. maybe there are some members on this board with 986 and 19" rims.

I don't think that lowering the car will have any effect on ABS or PSM

And last not least: IMHO 20" rims don't look good on a 986, I think the sweet spot is with 18", maybe 19", but that's just my opinion...