I use exactly the same set up as Ralph, 5 -6 feet of 10 -12 lbs maxima with a slow clear sink tip. I have caught them on 15 lbs maxima. They do not seem to care about the leader.
If the others were getting fish on longer leader, particularly with leaders in the 9-12 length, it may have been that they were getting down closer to the fish, i.e. the longer leader allowing the beaded fly to sink further and not be held up in the water column by their fly line. Obviously this all depends on the type of fly line, water depth, flow etc and may be very site specific to each angler. The way the fly moves in the water column will also depend on if you have a floating line or slow/intermediate sink tip as opposed to T11 etc, which will tend to trawl the bottom. Try casting further upstream and/or counting to 5 or 10 before stripping. Also try varying your strip, sometimes they just like a swing or a slow strip or a fast strip. It can vary during the day, or day to day. I have found a fairly quick strip to prompt that aggressive streak works well, especially if you put in a long 2-4 second pause in the middle of your retrieve, then start the fast strip again, you often get a hit on the drop or as the fly starts to move again.
For pinks, I do not think you need much of a sink tip, unless in very deep water. A floating line with 9' of 10-12 lbs maxima with a beaded fly should produce, or a slow sink tip and less leader.
With Coho, I tend to take a lot more care, with 3' 17/15, 3' 12/10 and then 3-4' 10/8 flouro.
Chum straight 5' of 15 lbs, if your rod can hold that freight train when it takes off!
GL