A and C
This is not a reason to not use Areoshell W15W50, it is a very good oil but like all things it has it's limitations, I run all four of my aircraft on W15W50 and have had no problems as long as the 50 hour oil change is done within the 50 hours.
What are your thoughts on doing more frequent oil changes regularly, say every 25 hours, specifically for lycomings in club aircraft, O-235/-320/-360.
Would that change if the engine was using D80/W80?
Are 5hr extensions to 50/150 checks a bad thing then, is it always better to go early? Accept the check will cost more per hour, but is better for the engine long-term.