Aftermarket wheels, and still have the summer tires on factory rims. It's a total PIA to have only one set, and I think abusive to the tire beads to repeatedly change back and forth. The factory rims with the factory mounted* summer tires have a lot less weighting. I'm comfortable with the aftermarkets, though, and now have great peace of mind with cold weather driving. On a cooler day earlier in the year with summer tires I managed to snap the rear, and thats's in spite of PSM and PTV. All these devices are compensating for loss of traction, so the "first line of defense" is to have the proper rubber meeting the road. The summer set will go back on maybe in March.
* The passenger rear picked up a sheet metal screw in Del Mar, California, ironically when I was driving to a self serve car wash. At first I was alarmed, but right next door was Clark's German Auto Repair. They declined repairing the flat because of time constrictions, but topped up the tire (a relatively slow leak) and sent me to a Discount Tire shop about a mile away. The place was great: very courteous to all the customers, quick to repair the flat, and when I went to pay, the service guy said, "Oh, no. Today's our free fix a flat day!" They also follow the Rubber Manufacturer's Association guidelines for repair and have a nationwide coverage guarantee. When I went out to the car, I smelled something like shoe polish: they had reblacked not only the repaired tire, but also the other three! I know a repair affects Porsche's speed rating, but took it in stride that it would help keep me out of
really big legal trouble. (I still went over 100 at opportune times.)
Minus 40 degrees... Is that Fahrenheit or Celsius?