I think x4 is too high. x3 is the maximum amount for me personally. Freeza can easily be double or triple the battle power that Piccolo stood no chance against and that Piccolo said made his previous forms look gentle in comparison to.
I still use the 3 million number in my battle powers...
The Daiz states that Kaioshin is stronger than Piccolo. This backs up what we see in the 25th, where Piccolo forfeits against Kaioshin.
Goku: 1,000
Yakon: 933
Vegeta: 667
Gohan: 500
Pocus: 467
Kaioshin: 333
Kibito: 315
Piccolo: 250
Trunks: 250
#18: 233
Goten: 233