Backing to flyline connections for the big boys have to be spot on, or you'll be replacing fly lines. The backing knot is a bimini with a two-turn surgeons double loop. Use a 30-turn on dacron and a 60 on gsp. This knot is close to 100 per cent and makes it easy to change fly lines if you use a loop in the fly line. The coated gsp is not 100 per cent because of knot slippage, but 65lb gsp backing, even at 80 per cent gives you 52lb strength. A 100 per cent loop for the fly line can be gained with a 50lb braided loop. This is a double catch loop with an eight-turn nail knot at the end of the braided loop.
Fly line to leader connection can also be loops. A 50lb braided loop on the fly line and a kreh loop in the leader gives you 100 per cent. Kreh loop or palomar for fly to tippet.
Lots of other rigging ways, but those are the ones that work for me.