With all of the injuries Vegeta had sustained, along with sacrificing some of his power to make the artificial moon, how strong do you have Oozaru Vegeta?
50-60k. Along with Kaioken x5 being used as the benchmark for him rather than something such as x10, it makes far more sense for his damage to be the most contributing factor of him weakening to the level a not overly enraged Gohan could put up a fight and not just him losing his tail.
Yeah, I'm just saying. Using x30 or 40 wasn't even on his mind in the Freeza Saga so he probably went with the improbable x5 but x10 didn't even cross his mind because that would be beyond absurd, especially in his state.