Let's not transform into a "Gohan's state vs. Dabura" debate. I think that i'm the only one who thinks that he was a SSj2, but let's drop it.
I have Goten at 80% of Gohan. He was able to equal Gohan in a sparring match, make him sweat, land a few good hits and even force him into the air. That counts for something, and Gohan said that Goten probably would be able to surpass him soon if he didn't train, so 80% is good for me. But i can accept 90% without any problem. The Daizenshuu states that Goten is as strong as Gohan, but i think that it meant potential.
Well, these are my battle powers
SSj Goten - 100
SSj Gohan - 120
Now, talking about Cell vs. Gohan. I think that Cell didn't increase his power any bit, only increased speed. As i said before, Gohan was able to block a hit like it was nothing, but Cell was kicked and was in the ground instantly.