On the West Coast here, we tend to run long bars with larger double dawgs... not just for big wood, but also safety. Most of us also run our oilers wide open on a saw, and it's well known to run two strokes WOT as much as you can, after break-in.
The MS261 is stingy on bar oil even with a wide open oiler, usually half a tank full after one tank of mix. Most will tell you running a 20" is borderline, almost too long for the saw to still cut strong enough.
I bought my MS261 as a package with a 20" Stihl bar with full-comp, full-chisel, Stihl Yellow chains... DISCLAIMER - Originally came with full-comp, semi-chisel, Stihl Green (safety) chain, but took them back to swap after realizing what they gave me when I got home.
After my MS261 woke up, it didn't take me long to realize this saw has more to offer. I proposed to my local dealer in running a longer bar with an increased bar oil solution. I now run a 24" Oregon bar converted from 3/8 to .325 by swapping noses with fs, fc chains. After researching on both our ends, they replaced the oiler 'standard' control bolt with a 'high-flo' control bolt from an MS460, giving about 30% more oil per spec... it's noticeable.
My setup is mostly for leaning Alders in mind... borecutting, hitting the trigger on them safely away with the longer bar. It also does well felling Doug Fir less than 24" in diam, bucking logs 8 to 16 feet all day long standing up, not bent over after limbing. Did I mention how light this saw is to pack around all day and how little mix it uses compared to larger saws?
I also run an MS462 with a 28" Stihl light bar that came with it for larger wood. Chains are fs,fc and fc,fc depending. I keep telling myself to pickup a 32" bar with a set of fs,fc chains but haven't been getting into big enough stuff lately.
My MS462 rips on a 28" bar with fs,fc chain, and I can tell a 32" bar with fs,fc chain will have no issues bucking larger Doug Fir. This saw has a full wrap handle, wish my MS261 did.
I used to run an 029 Super with an 044/046. The MS261 and MS462 compliments each other very well like an 029 Super did with an 044/046. A 60cc saw never made sense to me in a two-saw plan... 'goldilocks' is a one-thing for all plan.
A few more words, already TLTR... if you can scrub a chain better than factory, it will let you run the limits on a smaller saw with a longer bar than normal, so long as it can oil. If the oiler can't keep up and unable to modify, clean your kerfs more and run WOT a couple seconds before starting the buck. Maintain bars like a NAZI, no different than cutting only with sharp chain.
I get the reasoning converting from. .325 to 3/8 on the MS261 with a two saw plan to have same chain, files, sprockets etc. I kept mine as .325 since it cuts smooth as butter, not chattering like 3/8 does, when borecutting Alders or when limbing.
Cookie cutting is fun, but it's just drag racing.... it's not like trying to win the BAJA in a Raptor against all the elements, including driver fatigue.
I now run that Stihl Synthetic 50:1 with E0 in everything, but only run Stihl Motomix to run saws dry if not used for awhile. E0 is usually good up to 6 months and E10 up to three months if stored right. I use batches of mix within a week or two, rarely past that.
One more thing, read your instructions on the MS261 and MS462 M-Tronic saws. You'll find how to properly start them and warm them up which is different than non M-Tronic. Also, they have calibration procedures as well, and there is a tab for 'Winter' and 'Summer' mode.
Gratz on your saw and good luck with your journey!