For Goku's Kamehameha, Cell's Solar Kamehameha = 54.5366885 Septillion Megatons of TNT. SSJ2 Gohan >= Super Perfect Cell, and Vegeta stateed SSJ2 Goku > SSJ2 Gohan.
http://static.comicvine.com/uploads/original/12/129915/3064937-1429866076-gokus.gif
As a lowball, I will make Goku only 1.25x more powerful than Gohan. Which would make it like this
So overall it would look like this
-Base form: 681.70860625 Sextillion Megatons of TNT
-Super Saiya-Jin: 34.0854303125 Septillion Megatons of TNT
-Super Saiya-Jin 2: 68.170860625 Septillion Megatons of TNT
-Super Saiya-Jin 3: 272.6834425 Septillion Megatons of TNT
This is Goku's Super Kamehameha, he has an even more powerful version as a SSJ3 called True Kamehameha. Once agin as a lowball I will say it is only 1.25x more powerful than the Super Kamehameha. This gives it a yield of 340.854303125 Septillion Megatons of TNT.
The GBE of Rigel is
330.544 Septillion Megatons of TNT, destroying Rigel counts as Large Star level, and SSJ3 Goku's True Kamehameha is just a tiny bit above that (Even when lowballing it)
Goku also has the far superior 10x Kamehameha in this match. To determine its power I will use power levels (Sorry if they should not be used)
Goku had a power level of 910 when using the Super Kamehameha while his normal power level is 290. That is a 3.137931x boost.
Goku had a power level of 924 when using the Normal Kamehameha, at the time his power level was 416. That is a 2.22115x boost.
So the Super Kamehameha is 1.412750602x stronger than the normal Kamehameha. Which means SSJ4 Goku's normal Kamehameha = 1.544127843 Octillion Megatons of TNT. SSJ4 Goku's 10x Kamehameha is 15.44127843 Octillion Megatons of TNT. Which would make SSJ4 Goku a high 4-C using these stats
Does this seem accurate or does it take to many assumptions?