Actually I have to first say that my engine is a campro rojak.
Head from a Persona IAFM+. Pistons from BLm and were bored out very slightly. 76.5mm. Block is the same from 2009. My campro is the basic version. Very old.
It was overhauled last year to fit in the stuff i mentioned above.
So with that said, I did some digging to find out what oil is used in which variant.
Campro normal - 20w50 (IDK why so thick)
Campro IAFM (persona) - 10w30
Campro CPS - 10w30
Saga BLM 1.3 - 10w30 (if im not mistaken)
And apparently most of the later campro models actually calls for 10w30 post 2009. I seriously dont understand why.
Final verdict, since most campro block stays the same throughout the entire engine lineup, only difference from variant to variants are maybe the heads, intake manifolds and so on. What i think is, if the bottom end of engine is similar, then I also can safely use 10w30, 5w30, 0w30 like the other campro engine's brothers...? I may be wrong though, so apologies in advance.
Based on your explanation, I would go for 5W40 engine oil. To me, this dinosaur engine runs best using 5w40. Fuel consumption might be slightly higher but I really think Campro is best to run on 5w40.