Knawbone ...
this is just my opinion so take it for whhat its worth
I love a Myrtle riser , and my Miller has one that is just stunning . It may just be me but I believe that if you are using the lighter core woods , ie: 'bo and yew , a physically light myrtle riser works really well ...and it gives them , as Nate Steen says so well , a wand like quality ......
But I have also found that yew can vary in weight a fair bit so I'd ask Craig for his input
but
If you are going the heavier core lams , eg osage , I prefer a heavier riser wood as it alleviates some of the recoil IMO.