What if Kakarot didn't train on his way to Namek?
In a fight with Vegeta he has a power level of
8,150
So.. if he received a Zenkai he probably should be at 16,300.
Kaioken: 32,600
Kaioken x3: 48,900
Kaioken x4: 65,200
Kaioken x5: 81,500
I think he would be defeated against Gyniu. But then again he could get injured in a battle with the others, and then take a senzu bean to take a Zenkai. Then he'll beat Gyniu.
Vegeta jumped from 24,000 to 35,000 to 500,000 with Zenkais. If he uses the 3 Senzu beans the right way he could even go to high power level and fight Frieza.
But that's screwed up. Kakarot would give senzu beam to his friends. So he would die 