I think he should be way, way stronger than his old version.
Piano said that young Piccolo Daimao is so stronger than his old self that would be no comparison between their powers, and yet I don't think he knew that initial young Daimao (vs Goku) could power up even further, given his reaction of "fear?" when Goku initially knocked away Piccolo. Besides this, Piano was a bit nervous about Piccolo fighting Goku here:
This is completely different from his reaction when Goku knocked initial old Piccolo. Piano was just fine, because he knew that was not Piccolo's full power:
So I'd say that initial young Piccolo is already so stronger than his old self that there is no comparison between their powers.
Old Piccolo (100%) 10
initial young Piccolo 20
initial Goku (post Sacred Water) 24
Full power young Piccolo 36
Full Power Goku 37
Something like this, I guess.