If possible set up the texture mapping using two or three box/planar mappings instead of doing a UV unwrap.
With Rhino 7.5 and on these mappings are natively supported in Rhino Cycles (Rhino Render and Raytraced). UV unwrapped objects will get the textures baked, which is not ideal.
You’d set up mapping channel 1 for the regular grain direction. In case of Arroway textures you’d essentially do a planar mapping with the size of the texture, for instance one of the free textures Arariba Veneer Texture (wood 081v2) - Arroway Textures would have you a box with width and length of 36cm and 300cm respectively.
For the end grain do another planar mapping in mapping channel 2. The sides should probably also get their own mapping, which you can put in mapping channel 3.
You’d assign three different materials, for each mapping one: the main surface, the end grains, the sides. These you can assign with sub-object selection. And for each you can set the texture correctly and have them on the mapping channel you need them to be on.
That way you get best control and performance in Rhino 7.
Here a quick example - I was too lazy to match up the end grain with the main surface, but hopefully you get the idea.
