Well, I had issues running my 025s with .325 B&C. .325 tended to veer in the cuts and the bars got pinched. So I switched them over to Picco/Low profile B&C and rim drives. Easy to do, Stihl sells small mount B&C in Picco. Picco runs better and cuts faster because it has a narrower kerf, so you cut less wood. A lot less wood.
Enter the 026/260 saws which I started buying up right before and during the Great Recession (along with a lot of other saws). Easy to work on, and easy to port. About as cheap here used as the 025 was (around $200). Far easier to work on than any 1123 saws. Also metal side covers, engine frames, rim drives, and other pro features. Half my 026/260 saws (maybe a dozen in all) came with .325, and half with 3/8 std B&C. I tested same length and sharpness .325 vs. 3/8 std B&C one week in a huge pile of firewood and it was a dead heat. They have nearly the same kerf, so its the same work, regardless of profile or cutters per inch. So I flipped them all to 3/8 standard B&C and rims which is what my larger Stihl saws all ran with. One bar and chain size (3/8 std/0.050 gauge) and one file size needed (I round file everything), all interchangeable. So I ran the 026 fleet with 3/8 std B&C for several years.
Fast forward a few years. I was chatting with guys here on AS that were into chainsaw milling, they they raved about the low profile Picco B&C for large mount Stihl saws. Now historically, the only large mount Stihl saw that was ever sold in the US with a Picco B&C setup was the 024, and that was very short lived. Logosol also sold large mount Stihl Picco B&C on the US for a time with their chainsaw milling kits, but that was also discontinued. Basically Stihl found out that people were slapping Picco B&C on large saws like the 440 and running chainsaw mills with that setup, so they dropped that in the states fearing litigation (in case of failure). They continue to sell that setup in Europe though, and people there rave about it there. The large mount Picco/low profile bars are hard to get in the US west. For some reason some dealers had a larger stock of them in the eastern and Midwest US, especially in the 16 inch size. They come in 16, 18, and 20 inches. Canon also makes them now and calls them mini bars or super mini bars. I forget which. They tend to be expensive though, if you can find them. I found some new old stock large mount Picco bars online and I bought a pair of them. I also stumbled across some Picco rim drives for the o26 at the Stihl shop in Cottage Grove, OR that stocks a lot of older saw parts. Then I ran Picco PM (now called PM3) chain and it ran OK. PM is semi-chisel green safety. I then flipped to non-safety low profile semi-chisel re-branded Carlton sold by Baileys as 'Woodland Pro.' That cuts a lot better. But still not fantastic.
So... fast forward again to a couple years ago, and Stihl came out with their new Picco full chisel non-safety PS loops, and whallah! My 026 Picco B&C saw was reborn. It is my new favorite setup. Fast and nimble, cuts anything in a hurry. No BS firewood saw. Perfect compliment to one of my lightly modified 361 saws. Cutting in crud I still flip them to semi-chisel and they stay sharp a lot longer. I also got a loop of the new full chisel non-safety PS Picco for my 211 saw (same power as the earlier model 023) but it does not pull that as well. PS is aggressive stuff, well suited to the 026. It would probably do well on an 025, and certainly beat .325 on that saw. Never tried that though, as I sold my last 025 long before PS chain came out. I love my 026 saws with Picco B&C. I do not run anything else on them any more.
Stihl sells an upgrade kit for the 261 in Europe with the Picco B&C and rim, but not here in the states. The part numbers for the large mount Stihl Picco bars are (or were) as follows:
16": 3003 000 6313
18": 3003 000 6317
20": 3003 000 6321
