How strong can a non-Super Saiyan get?

[Super Neko Majin Z]

How strong can a Saiyan get before they use SSJ for the first time? Is there a limit at all? Tell me what you think, I love questions like this.

 

[Jerk Store]

However strong the plot demands. Look at Cabba.

 

[SSJ2]

Potentially stronger than any SSJ considering they can receive zenkai.