My uncle has been using Opti oil at 100-1 in his Stihl 024 for over 30 years as a firewood saw, and I can attest that it still runs strong. HOWEVER, he has been warned that he should run a thicker oil mix by a dealer to prevent internal rust when the saw sits unused for a long period, as 100-1 will not have enough oil to properly protect the saw. I don't Opti myself, but have tried Amsoil at 100-1 with no ill effects. What impressed me about Amsoil was how concentrated it was compared to regular dino stuff, you have to make sure you shake up the mix well to distribute the oil properly. If I used a saw commercially, I would probably use a synthetic mixed somewhere between 50-70 to 1, and not worry about internal wear.