OBL mysteries : the real limits

I want to organize my guest blogging. To get high quality backlinks, I know I need low OBL websites.

I searched in the whole forum for hints about the OBL restrictions and find some clues (that seem contradictory):

1. The OBL must be 20% of a whole site or it’s not worth it.

2. No more than 20-30 OBL per site.

3. The OBL ratio is per page.

4. No more than 3-5 OBL per page.

Is there a veteran(s) that could share his(their) experience about these rules?

I want to organize my guest blogging. To get high quality backlinks, I know I need low OBL websites.

I searched in the whole forum for hints about the OBL restrictions and find some clues (that seem contradictory):

1. The OBL must be 20% of a whole site or it's not worth it.

2. No more than 20-30 OBL per site.

3. The OBL ratio is per page.

4. No more than 3-5 OBL per page.

Is there a veteran(s) that could share his(their) experience about these rules?