I have owned all of them and there are advantages and disadvantages to each model. But to answer your ? simply the 385/390 and the 395 all have the same stroke 38mm or 1.5 " now the 385 has a non windowed 54mm piston , the 390 has a 55mm non windowed piston and both 385 & 390 have inboard clutches and the chain tensionier in the side cover of the saw. Also the 385/390 is about 16lbs dry which is about 2lbs lighter than a 395 at 18lbs dry now these weights are true weights of the saw not the factory advertisment. Now the 395 has a 56mm windowed piston , an out board clutch with the chain tensioner in the body of the saw. So there I gave you the specs and differences. The only thing that makes a 390 better than a 395 is in stock form the power to weight ratio is higher and the easier access to the chain tension adjustment screw. But the 395 is made very very well it is one of the toughest saws ever made and for a long bar saw it's hard to beat. The 395 is a torque saw for cutting big trees all day or milling. I am actually building a 390xp with a 56mm bore and a 2100 thin ring piston if I can locate one. If not I will use a Meteor 395 piston. So I hope all this garble of info I just spit out help you to answer your question.
Thanks for taking the time to explain the differences.