IMO and experience with Apex and Nytro with MCX and shim, your good to 14 lbs easy at elevation (5000 to 7000 +). A buddy of mine runs 15lbs on pump premium, 4000kms on his sled and all is well. Im sure you go 16ish, but i wouldnt push it. The last 2 years, and again this year i run 100LL AV from 14 to 18lbs and my motors were still mint. No leakage after 4400 kms on one and 3600 on the other. I know theres the big debate on AV vs vp C12, dont care to get into, im not a fuel expert but between the miles i have put on using AV and all my buddys i know first hand it works great for us.
The joy of the MCX is it comes set up on the safe side, reliable as a mofo and day in day out works awesome. Im sure they could send it out leaner, but then you run the risk of reliability IMO.
