No knot, despite claims, will hold 100 % of rated line strength. A properly tied and lubricated 5 turn improved cinch should hold 80-90% but if you have an "Ooops!" or a "WTF did that loop go to??" as I often do, can drop the knot strength down to as low as 60%. With my beat to hell hands and fingers I've recently switched to using a 5 turn uni knot to tie flies to tippet. This is after 45 yrs of usin' the improved cinch. It's about the same strength as the IC and a tad easier for me to tie. I use a 5 turn duncan loop for streamers and soft hacks anyway and the uni is similar except you throw the loop in the tag not the running line.
One thing about knots... practice throwing them @ home until you're proficient, I use a chunk of old fly line. Standin' in the stream with risin' fish all around you is no time to try and remember a new to you knot.