Wider tire upfront on gravel? Yes? No?

[makoti]

I am running 38 GravelKing SS+ with cushcore inserts (not sure I'll keep using them when the wear out - if they do) and want to try wider tires. My frame is limited to 42-42 on the rear, but the front is very flexible.
I don't want to push the max in the back and end up trashing the chainstays if it gets sloppy, so was thinking only bumping up the front. They make a 43 SS+ (no 40).
Would running the 43 front and 38 rear work? Is that too large a difference? Anyone do this and can comment about that kind of a difference? Worth it?

EDIT: no idea if it matters, but more info is good. Shamal Carbon, 21mm internal