Fodder or Merge?

I just got my third Surtr, and I can't decide whether or not to merge him into my +1 +Res/-Spd Surtr.
I've already given my first Surtr DC, so another point of Atk and Res on him sounds really good, but I want to know if it would be better to fodder SS4 to Xander/Camus.

(P.S. I don't already have a Xander/Camus leveled up.)