Got this update on a test from Ellis Amdur:

Oak (Sessile AKA English Brown Oak – Quercus petraea) – Its qualities are similar to American  Oak rather than kashi.  The grain is rather wild. I received a thick straight bokken, very well crafted.  I tested it against a Japanese kashi bokken.  At 20% strength impact, the Sessile Oak bokken dented rather deeply, while there were no dents in the kashi bokken.  We increased the impact to about 30-40% and there was a marked difference in the feel of the weapons. Kashi absorbs shock, whereas the Sessile Oak “rings” unpleasantly in the hands.  At the fourth impact, it broke at an angle along the grain line, as if was cut.  I do not recommend this wood for weapons.  Janka Hardness Scale  1120