Hi Charlie, I have lots of linen backed posters, most of the larger variety (3sht, 6sht, 2F, 4F, but many 1 sheets too). Also Thierry hates "French Grande"
The linen backer of these, who was also a poster dealer, always allowed 2 inches excess on each side for all posters. I store these rolled in a tube, often many together and I am surprised how crumpled some can get and I am grateful for that excess. The added crumpling probably happens if all posters are not rolled and aligned exactly flush on the one end they stand on (I don't have space lie them flat plus they might get waves in them like that). I wouldn't want excess linen any less than one inch on each side (I am happy with the two I have) and thus would not let a frame trim less than to 1". Sometimes a poster looks nice with a matt around the poster and larger excess linen I assume can be under it. If there weren't many other posters for sale I wouldn't think the selling price would be affected if it was trimmed very close to the edge, otherwise for me yes affected. European linen I believe is a thin linen and I can imagine that may fray easily.