That's actually a good point that I over looked. the Cell Jr's did prove to be a tough fight for Goku even if he wasn't at full strength. Considering Gohan basically crushed them to dust, that might be proof that Goku wasn't strong enough even at full power.
This is exactly what they said.
Goku: Gohan, you thought i was holding back because you were comparing my energy to yours.
Piccolo: Is that true, Gohan?
Gohan: Yeah, it's true.
As far as could goku have killed cell to begin with, he might have been able to.
Goku does say somewhere "I wanted to give Gohan the chance to save the world."
I think that says it all, Goku could probably have won but he didn't want to. He wanted to let his son win.
lol I'm sorry but its obvious Goku has no chance in hell of beating Cell. First of all Cell is not even fully powered up when he is fighting goku, he is still holding back, Secondly Goku is shattered when he ends the fight and cell offers him a chance to take a Senzu bean, this should tell you that he is very confident and knows Goku dosn't have a chance in hell of beating him ... And if I'm frankly honest when cell comes back after his self-destruction, he should easily beat Gohan ... I mean one of his attacks renders Gohan unable to use one of his arms and severly weakens him. But i guess the good guys always need to win .... 
Cell is a noob and you know it. 
The only reason i believe GT was so terrible was because it wasn't even written by Akira...
Here is a question for all you dragon ball fans, How much different would the DB universe be if Krillin had killed Vegeta when he had the chance at the end of the first saga?
-Namek Saga-
Without Vegeta to slow their progress, Gohan and Krillin would've been killed by the Ginyu Force on Namek, and Piccolo would never have been revived by their efforts. The Earth's dragonballs would remain lost. Goku would arrive to find his best friend and son dead, and wipe out the Ginyu Force without a second thought. I'd give his rage so much credit to assume he'd Super Saiyan upon arrival or at least wipe out Ginyu before any body swaps. As for Bulma, I'd give her 50/50. It's likely Goku would've sent her home, but who's to say?
-Android Saga-
Had Goku defeated Freiza anyway, he'd have returned to Earth alone to square off against King Cold and son, but likely not before more causalities (minor characters like Chichi and Roshi, no doubt). Had he defeated them, he'd have died later of the heart virus because with no Vegeta, there's no Trunks to go back in time to give Goku the medicine. Dr. Gero, plans of murder foiled by nature, would've gone about his plans much in line from the Future Trunks timeline. He'll be killed by his own creations and they'll go about terrorizing the world. Cell may manage to obtain his perfect form, but without an adequate source of strong fighters to absorb, or even a healthy human population this is doubtful. If he manages, he'll likely destroy Earth for kicks and leave to terrorize the universe, if not, 17 and 18 will likely destroy him.
-Buu Saga-
Years later, Babidi will arrive with Dabura. With no sutable fighters to restore Buu, Babidi will send Dabura to hunt down the android, or a hidden Cell assuming he still lives to gather the energy. However, I find it more likely that Babidi will betray Dabura and obtain the required energy from him, since he and Gohan fought on roughly even terms, and Gohan was enough to do the job. Buu would be revived into a dead world and have no real reason to go about on his reign of terror. Babidi, likely unsatisfied with a world full of.... nothing, will take Buu, hop in his space ship, and look for inhabited worlds to conquer.
Thx Hazel and Costa
Wow, that was a very informative and well thought out answer.
Fight.Power, you have to remember that goku wasn't at full strength when he fought the cell JR's. After his fight with cell, he didn't take a senzu bean until gohan killed the cell jr's