I've been using Synpower 5w30 SM in a vehicle that specs 5w20 for a while without issue.
However, it is sluggish, even compared to other 5w30 oils. The SN version is even heavier than the SM.
So in your situation, I would consider getting some xW20 (eg PP which has 2 rebates right now making it very cheap) and mixing into subsequent changes if your first oil change with 100% Synpower isn't to your liking.
And even if Synpower is ok, you've got some nice PP xW20 for when your Synpower finishes.