As far as walnut, elm, or whatever used for the core of a tri-lam... I don't think it makes a whole lot of difference when choosing between those in the midrange... say with a specific gravity of .50 to .70. This would include woods such as yew, walnut, elm, ash, mulberry, cherry, hackberry, hickory, oak, hhb, black locust, hard/rock/sugar maple, etc. Are some slightly better than others? Yeah, undoubtedly. I know I have my preferences. But not by a lot. Keep in mind, there can be differences within a single species that can mean almost as much.
Basically, it's not a whole lot different than the differences between these same woods in a glass/wood laminated bow. Instead of the glass doing most of the work... the bamboo and belly lamination does it. The core material matters... but matters less than the back and belly.
I like osage and those at the upper end of 'the others' for the core simply because I often like my bows petite, stressed, and heavy in draw weight... and osage delivers... though I have and will continue to use others.
So many bows... so little time.
Wish I was retired like Ol' Roy.
He'd be completely SICK of me by now