Dear Pete and Steve,
The heavier line weights and faster rods have nothing whatsoever to do with the fish themselves. The stiffer rod isn't for fighting fish. As Tim Murphy says, the fish are dumb, and if you get a fly to them, it makes not one iota of difference whether it was thrown on a 5 wt or a 2 wt, and they're small, so in fighting them, likewise it makes not one iota of difference.
The key is getting a fly to them before getting so close as to spook them. Now, skill is still far more important than equipment, but if you do look for an advantage in equipment, it's in casting. Distance in tight places is the name of the game, all of the equipment, and all of the skill of the angler, is geared towards this end. And when I say tight places, we're talking streams that you can jump across, in a tunnel of rhododendron or other such brush.
You have to cast through some small spaces, under overhanging limbs, etc. And all this with no backcast. Tight loops help. Thats my whole point. A rod doesn't have to be overly "powerful" in the distance casting sense, but it should be "punchy", i.e. capable of throwing tight loops on short casts without much motion to make it happen.
For what its worth, my rod for these streams is a 4/5 wt, and I load it with 6 wt line. There is absolutely no question that such an approach has allowed me to catch some fish I wouldn't have otherwise been able to catch.