Yeah the speed is amazing, a 4k texture with no noise whatsoever takes about a minute ;) I think it just uses the draw order of UV islands. So you could just offset their coordinates outside of the 0-1 range. What seams do you mean, smooth group splits or UV seams ? I haven't really noticed a problem there.
Thanks everyone! Contrails: Very slowly! I have a scratches brush that looks like a square with one of it's corners partially erased, and a very high rotation jitter, as well as a size controlled by pen pressure. I know I didn't come up with that idea; I think it's from someone on this forum. Anyways, I draw with a low…