I am one of those fellows who have had very good experience with efco = oleo mac products. I have a few chainsaws, etc.
I am not sure which models are still available in the us but the ones I have are, although still produced today, old school technology compared to Stihl & Husqvarna. That is also the reason I took them, no bling bling to break anytime soon. Nevertheless tough as nails in real life cutting scenarios. Although I have to add that my dealer has the full range and I am not afraid of them deleting it anytime soon. Further I live not to far from Italy so not much to worry about for me.
Your Dolmar 5105 is enough for your needs! Learn how to sharpen your chain well, buy QUALITY!!! (Stihl or high line Oregon stuff NOT noname el cheapo stuff) chain, Keep the chain out of the dirt and run your saw like you stole it after your break in time (~10-20 refills) and a proper carb retune. The 5105 is a real powerful 50cc animal and will not let you down. I see, from your description, it as totally senseless to buy a 60cc or larger saw. I assume your bar length to be 18 Inch which will be absolutely good enough up to 30inch tree's.
I know, I know! This is a totally new concept and unimaginable for many members on AS, but it is true! You CAN cut a tree from both sides...
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