Ok, since it looks like I'm the only one that absolutely loves new oil threads here, I'll share my experience, although not with my Z (only 19k miles). I have a Jeep Commander 4x4 with the Hemi 5.7 that has about as many miles as your Z. I've always used Mobil 1 syn oil products in it since new, however, now I'm using the high mileage flavor with corresponding M1 hm filter. Seems to be treating my engine well. Not much burn between changes. Still runs like new. I love that Jeep!!!
I know this reply doesn't directly address your question 100%, but it does hit somewhere about the target. Hope this helps.
