+1 I've used both .325 and 3/8 chain on my 026/260 saws; and have finally converted all my saws to 3/8". It simplifies my going to the field with bars, drive sprockets, chains, etc all being compatible and interchangeable. And I only have to buy and stock one size chain, bar, sprocket, etc. instead of two of everything.
A muffler modded 026/026 pro/260 Pro will pull an 16" 18" or 20" bar with ease in hard wood where I live. I prefer the 18" bar myself, others, who don't like to bend over, run the 20" with good results. I think its really a matter of preference, and you will soon know what your own preference is going to be. Great saws, buy and enjoy.