I'd go with
Xeno Black estimate of 30-35 billion based on the average human having a power level of 5. That's a big range so it could account for some outlier super humans we've seen in DB. There's no way to be sure how that compares to the most powerful Z fighters but I'm going to try and come up with a bare minimum estimate of how powerful later characters were.
Initial SSJ Goku: 150 million
From the Daizenshuu and we'll use that as a starting point.
#17, #18, and Post-powerup Imperfect Cell: +150 million
All confirmed to be stronger than Goku.
Semi-Perfect Cell: +300 million
He was clearly more than the sum of his parts but at the bare minimum he was at least Imperfect Cell + #17.
ASSJ Vegeta: +300 million
FPSSJ Goku: +600 million
Vegeta knew Goku was more powerful than he was when he sensed his 50% level so that means 100% Goku is at least 2x stronger than ASSJ Vegeta.
SSJ2 Gohan: +1,200 million
At the bare minimum, SSJ2 is 2x SSJ1. I think it's something like 5-10x at least but 2x is the lowest possible estimate.
SSJ3 Goku: +4,800 million
At the very least, SSJ3 is 4x SSJ2.
Buuhan= +9,600 million
Base Super Buu and Ultimate Gohan were both stronger than SSJ3 Goku so together they would be at least 2x more powerful.
SSJ1 Vegetto= +9,600 million
SSJ2 Vegetto= +19,200 million
SSJ3 Vegetto= +76,800 million
SSJ God Goku: +77,000 million
Goku assumed fusion wouldn't work so stronger than what he estimated Vegetto's full power to be.
Beerus: +127,800 million
In BoG, Goku was a 6 and Beerus was a 10 so Beerus was 66% more powerful.
Whis: +192,000 million
Whis was a 15 so 50% higher.
It's crazy how inflated power levels became considering this is the most conservative estimate possible. It's still way too low since I can't imagine the Fused Super Human surpassing SSJ2 Vegetto. I assume FPSSJ Goku was at least 10x stronger than he was on Namek when he first became a SSJ. That would put this Super Human between SSJ1 and SSJ2 Vegetto. There are a lot of other factors to consider like Goku being a "FP"SSJ2 during the Buu saga so much stronger than Cell Games Gohan and the gap between all the characters which could fit with many different estimates. I guess most likely the Super Human would be somewhere between a SSJ2 and 3.