Salmon are starting to run in the river around here and I was thinking of trying some Power Pro 50lb or something like that for them. Question is being a leader is need with this stuff, say I were to run 20lb mono or floro what strength do I actually have at the knot? I know different knots have different breaking strengths but whats the point in 50lb braid if you only have 20lb hold your lure on? Last salmon I had on broke my line at the lure with 20lb mono.

Get a long, limber rod, and tie good knots.  The fish below was caught last week on a Lamiglass 9'6" ML/moderate rod with 8# mono main and 8# FC leader using a small Spro swivel.

Couple questions, whats a rod like that cost, and why the FC leader over mono? How long did it take to land that fish?

Just like bass rods, they run anywhere from $40 on up to hundreds.  The Lamiglas I use was around $140.  The FC leader is very tough material, and much more resistant to breaking than mono.  The fish take anywhere from 10-30 minutes to bring in.  There were at least three that were over 30# in the pool we were fishing, and they are impossible to land, LOL.  My buddy had one of the monsters on for about a half hour, and it broke off at his feet.