I think weighted Goku being at 91% of Tenshinhan is a bit too close. Goku said Tenshinhan was way faster than before, so I'd like to see it at least as a "monster Zarbon ~ Vegeta 24k" gap. Maybe 87% also works, but I wouldn't go with less than that.
An interesting way to figure out how strong Piccolo Daimao got when regaining his youth: just try to estimate the gap between Tambourine and Drum... Drum should be stronger than Tambourine by the same amount young Piccolo should be stronger than old Piccolo IMO.
Tenshinhan also says Goku didn't use anywhere close to his full power. So Goku [vs Tenshinhan] being at 80% of Goku [Tenshinhan's estimations] seems like a bit too much. Kami did say Piccolo Junior was way stronger than him, yet they were seemingly fighting evenly... I'd think Kami did know Piccolo was hiding powers and was estimating his power based on his reserves, yet he seemed pretty surprised when he saw Piccolo vs Goku. Piccolo (true power) >> Piccolo (Kami's estimations) >>> Kami sounds fair imo. I think Piccolo begun fighting Goku with the same amount Kami guessed his full power would be.
Tambourine 75
Son Goku 100
Drum 140
Old Piccolo 500
Young Piccolo 940
Goku (post Water) 970
Goku weighted (speed) 1,000
Tenshinhan 1,200
Goku unweighted (vs Tenshinhan) 1,800
Goku (Tenshinhan's estimations) 3,000
Shen/Piccolo Junior 4,500
Kami 5,000
Piccolo Junior (Kami's estimations/vs Goku) 7,000
Piccolo Junior (full power) 12,000