Better to target temperature rather than fan %. Under 70°C is recommended, personally I have all my cards target 66°C which is easy to achieve in most cases.

Depending how your cards sit some fans will run at 35% some at 80%, but fans are cheaper to replace than silicon, so don't worry if they are at a higher percentage on your rig.

For AMD I use  OverdriveNTool to set a target temperature.