He'd be 50% stronger.
He'd be the same strength, he wouldn't get stronger than anyone who is currently stronger than him (Madara, Obito, Hashirama) even if he had all of Kurama's chakra.
Well, it isn't just more chakra... It's yin chakra. Meaning, it strengthens Kurama's current yang chakra.
Think of it as a missing ingredient in a recipe.
So it might increase the power of Naruto's attacks.
So now he has 66.67% of Kurama's chakra?
Kurama getting its chakra back might increase the size of his Bijuu cloak I believe thus increasing range and physical strength so I guess the only attack that would get stronger is his Bijuu Dama and physical strength (Bijuu cloak)