Most recommend that Stihl chain be sharpened at 30 degres with a zero offset (90 degrees, or flat across). That said, I notice that most of my Stihl chains come from the factory sharpened at 35 degrees, zero offset. 35 degees will cut faster but also dull faster. I have had some .325 small mount bar chain sharpened at 25 dergees on some of my previous Stihl saws for some reason, but that seems pretty low of an angle. I do not use .325 any more and I switched all my large mout Stihl saws to 3/8 sandard bars and chains.
Cut them at 30 degrees 60 on the tilt now anything from 25-35 will work the closer you get to 35 the more aggressive it will be. If your saw has less horse power you want to be closer to the 25 degrees.