right now, the system is ok. I plan on putting another three cameras down there. I foresee the biggest problem being the cameras will all have to daisy chain through the one repeater. I think the biggest problem is lack of cell service. If I had cell service in that area and could put the Cell cam in the middle of it, I would be Ok. As it is, the cell service is only on the very NE corner - so every camera has to send that direction.
I put my cell unit on top of a ridge that is 80-100ft above most of the cameras. This gets me link levels in the 90s to a camera 150yds away and below it, in the 60s up to 250yds away. In comparison, another camera 250yds away but at similar elevation (signal must go through trees the whole way) was in the 40s.
When you say "usable" signal level, YMMV. My cameras don't get the level of traffic others here get, but I have a camera that runs level 12-16 most of the time and it doesn't seem to impact getting pics.