For a 50lber in yew, I wouldn't go more than 28mm wide, unless its really light thick ringed yew, then 32mm for an ELB( I have made 55-60lbers from 1" wide fine ringed yew).
Rough the stave down to 35-40mm like you have marked out, that should still give you plenty of meat to reassess the knots, and how they run. Then rework down to 28-32mm wide depending upon the quality of the stave,
My personal approach with any knots regardless of the species, is to leave extra wood around the width at that point., and the depth too when roughing out.
Now many people just shave it off flat down to the layout line, right through the knot and still get good shooting bows. Then they fill any hole with a dutch plug. Some people do the same thing but end up with firewood. Regardless yew seems to tolerate a little more grain violation, and pins than most other bow woods, but push it too far and it still breaks.