I have 7:1, with the becket at the top and combined 3 plus 1 at the bottom and a triple with ratchet at the top. It is a modification of a harken 8:1 system, as I found that the ratchet on the bottom of the system won't hold much weight as it only wraps around the load ratchet about 100 degrees. I have another ratchet on the upper block as well now and it worked really well during a recent blow in bendigo.
To attach to the boom, I have a dyneema (?) loop inside plastic fuel hose which goes around the boom similar to the A class. I don't trust hangers on a point load, and if you put a flat side shackle in the loop you can attach it to your out haul slot to get the perfect position. I am really happy with this set up now after a bit of mucking around.