The Wix and equiv. versions of the B50 have the 12-15 micron rating.
That is why you want to run a true Hastings/Baldwin B50 (or B164) filter. They are rated MUCH better then that.
I believe the rating is 2 nominal, 8 absolute. I haven’t looked at specs in a long, long time. I'm sure you can dig them up though.
There is still a major debate about the need for sub-micronic filtration. While I have to agree that more filtration is gooder (duh?), the actual cost to get to that submicronic filtration does not justify the ends. Lets keep things in perspective:
Human hair - 80 Micron
Human Red Blood Cell - 8 Micron
B-50 Filtering Efficiency - 8 Micron
Most of the reading I have done puts the damage particles at +/- 12 Micron. Some say as high as 25 micron (which is where most full-flow filters will filter to). Hydraulic fluids are down around 2-3 micron.
Think of it as more of a curve. The higher the micron, the higher the wear. As you decrease micron size floating in the oil, you decrease wear. At some point, you reach a spot on the graph where lowering micron makes a minimal difference in wear. It is there. It may even be measurable. But it doesn't justify the costs of replacement filters PLUS replacement oil.
I just bought 13 quarts of Amsoil’s new CJ-4 oil. At $130, I'm going to do everything in my freaking power to make sure I have to put as few make-up quarts of oil in that ole engine as humanly possible.