Why do you think M1 is not a true synthetic?
Where is the nearest Valvoline refinery?
Here is an interesting thread for you to read:
-54C Pour Point and high PAO content - Bob Is The Oil Guy
Have you done analyses before/after, or do you intend to? That's the only way of knowing.
The post got me thinking. Which M1 did you use, and which Valvoline have you switched in? Are you using the factory recommended OCIs (after the TSB on oil from SOA)? Oh -- I haven't actually answered the question! IMO no, you won't have a problem.