Thanks for summary, skitron and trumpet. There is nothing called portrait focal length and dof. Companies define that for simplicity sake (for simple minded client) and keeping real life reproduction in mind. At least for me, art photography is not about that. Focal length as well as dof are just a tool. I hope painting forum does not argue that size 1 brush is better that 2 for masterpieces. But you are allowed to say that this is my favorite focal length for portraits.
However, I disagree on subtle difference point. If you are able to see the subtle differences, it can be like tiny sand particle in eye. For people who can't see them, world is bliss. Passion for perfection is engine of creation. Life and things are usually not dramatic.
Specifically, the dof at f/2 vs f/3.5 for 135 @ 10 ft is .19 vs .32. thats not subtle mathematically, about 1.7 times more. But I get yr point, dof difference is visually subtle (still important to few), f/2 to f/3.5 can be difference between photo and no photo in certain low light situations.