Looks like you have received great advice already, Fox.
Unless you are going to be hitting some hickory over 20", Stihl 066 or equivalent Husky (as mentioned) should do the trick. You have to make the call, however, above that level of toughness. Big Hickory or Live Oak, for example, are very demanding. As Oregon said, you won't be unhappy with too much power.
If you ask, "What is the biggest stuff I would ever want to cut?", you may start picturing a table top made of bookmatched, butterfly-jointed 30" slabs from the flare of a Red Cypress stump. If that's the case, get ready for Stihl 088, a used Stihl 090, or a Husky 3120.
Happy shopping!
Phil L.