See the attached photos. Click on the photo to enlarge.
Tim, I've used both brushes recently, and here are my observations. The knot measurements (as mounted in these two handles) of the SynBad are 61mm tall and 30mm at the base of the fibers at the top of the glue plug. The SilkSmoke is 56mm tall and also 30mm at the top of the glue plug.
Both brushes are amply packed to the point of maintaining an adequate amount of backbone which is common in most quality badger and boar brushes. I have owned and used several other synthetic brushes in which backbone is slim or none.
In a subjective sense, the SynBad is as soft as a cloud when stroking the cheek when dry. The SilkSmoke is also soft, but minutely less than the SynBad. On the other hand, my SilkSmoke has no sensation of scritch if the dry brush is pressed and stroked against the dry cheek, while my SynBad has a minimal or even negligible scritch when the dry brush is pressed and stroked against the dry cheek. The SynBad fibers appear to be somewhat finer and more thoroughly packed than the SilkSmoke. (This is my brush and my cheek, and I'm doing the stroking, so perhaps others may certainly disagree.) Furthermore, the crown of the SilkSmoke has been physically trimmed/shaped in a configuration that just seems more subjectively attractive to me.
Both brushes are virtuoso at manufacturing thick and rich lather with competent soaps. I am attaching photos that show the visual differences between the two brushes. SilkSmoke is gray and SynBad is brown.