its my foggy memory that says " US M030" does not lower the car.. but it does stiffen it. Only the ROW (rest of world) M030 lowers the car. At least that's how it was on the Boxster, so I figure the same for the 996?

Again, you are talking 10mm difference from stock.. that's less than 1/2 inch. Heck, you could find a 10mm difference just between two different brands of the same size! They will be fine. OEM is fine too