Mantis, et al., I could tell you stories about my Mac 610 forever, because most of them are such pleasant memories. Here's a small one for you that's on the house:
This saw was a champion of its time and ran circles around most of the saws made back in the '70s. Right after I bought it, LOML and I started a small firewood business trying help make ends meet. We both worked together at it with her running a little Mac for limbing and me using the big Timberbear for felling and bucking. I was so proud to be the owner of this saw that I could burst.
Biggest tree I ever dropped with the 610 was a red oak growing in Connecticut. Gypsy moths had completely defoliated it for two consecutive years and on the third year, it never leafed out and died. So, I dropped it by myself with the 610, LOML as my witness. It must have been 30" across at the base and fully branched. Just before it hit the ground, I cut the engine so that I could hear the crash and feel the earth shake around me.
That tree was rather easy to split (typical of red oak), and I did it all by hand using an 8-lb splitting maul. The first branch was at least 20" across and I had to be really careful removing it because it was pointing skyward and as big as many trees surrounding it. That was like a second felling job. The wood was sold to five customers who were so happy to receive split red oak that most of them doubled their initial orders.
The Mac 610 has served me well through the years, but I must admit that technology eventually caught up and passed it. Regardless, many of these saws survive today and never fail to raise the eyebrows of Stihl owners who enjoy watching "the old man" in action. That includes me.