F
Fisherman.Z.
Honestly, your 6 wt should be capable of landing a steelhead. A fatty steelie (10 to 14 lbs) might push you to your limits during the heat of the fight but with enough patience it will run out of gas. With lighter gear you'll have to choose your beaching site well if you didn't have a net handy.
Being said, I went from a 5 wt to an 8wt when I got a rod specifically for metalheads.
So when in doubt get both...