If you want a perfect alignment, either do it yourself with strings, or take it to a race shop that knows Porsche
My "guy" takes 3-3.5 hours, charges $300 and is far better than ANY alignment rack.
Trust me, it makes a huge difference. Before my alignment with the best "tire shop" alignment could get, the car didn't really want to rotate. After the string alignment, I almost spun the car the first corner I took with a bit of speed. Of course it probably didn't hurt that I put in a M030 ROW suspension and camber plates in the front as well
The laser racks are only as good as the calibration and most of them probably are close, but not spot on. Most fo what they do are street cars and close is good enough.