I've put a lot of thought into this myself.

After due consideration, I think I'll stick with the stock rubbers. I've spaced mine once at about 7000km, and believe I'll get about 40k out of them.

I think the driveline is designed to have rubbers that 'give' to absorb shock, and bearing in mind the fact that Tenere gearboxes, for whatever reason(s), are occasionally a bit fragile, I'll stick with oem until I'm convinced the poly ones are as effective.

Where poly has replaced rubber in engine mounts and car suspension components there is proof they can contribute to harshness and so on. Part of that proof is found in my own experiences.

It's equally true that the oem Yamaha driveline rubbers are under-specced, or we wouldn't have to space them up. However, once spaced (I've used rubber belting cut to shape), they seem to hang in there ok.