Having spent in excess of 15 years on a sewing machine, you are much better to throw your tarp over a substantial rope, say 12mm maybe, than hang it from loops or expect the guy ropes to hold it. Even better if you can find a decent ridge pole, clean it up nicely and throw your tarp over that. In excess of 4 metres is a lot of strain on a piece of fabric. I use to make my big fly's with either a decent tape ridge line, or an extra layer of fabric along the ridge line to take a bit of wear. Find a good manufacturer/canvas guy and have one made. TwinNeedles may be worth talking to.
Bookmarks