Measurements from different manufacturers are all conformant to ISO527, So you can pick the top product and be sure of its characterisitcs.

Martin can you clear this out for me, I didn't understand from your post : are they injecting sillicon rubber into PEEK mould or the other way around ?
It would be interesting having the block sideplates injection molded, it will save a lot of fabrication time, and much less material wastage.