There's no really much life on Kaio's planet, so I honestly don't think it would be very strong. I mean Goku after taking energy from Earth and even the sun was only about strong enough to beat Oozaru Vegeta (before it was weakened), so for all I know Kaio's planet might actually make a Spirit Bomb even weaker than Goku himself. Unless the creators power goes into it, in which case I'd say around 9k.