I think you’ll find that most of us have caught salmon both in and out of the “preferred” temperature range. I’ve caught kings throughout the entire water column, so I try not to get too locked into a single number.
Here’s a typical starting 6-rod spread for two people:
Riggers- Usually spoons, stacked. I’ll run one rigger in the 50–54°F range and the other below, like Gary mentioned.
Divers- Typically flasher/fly or flasher/meat. I’ll run one in the cold water (around 42°F, give or take) and the other in the 48–56°F range. The Smart Troll system makes it much easier to know exactly where those presentations are running.
Planer Boards- Spoons, flasher/fly, or flasher/meat on lead core or copper. The length depends on where my target temperature is that day.
From there, I let the fish dictate the program. I’ve caught salmon in water as warm as 65°F. Temperature is a great starting point, but it’s only one piece of the puzzle.
Use your electronics. Pay attention to bait, marks, currents, your speed, and when/where you’re getting bites. The fish will tell you what they want, and just as importantly, what they don’t.
If I have a third or fourth person on board, I’ll add a few more rods to complement the spread, divers or coppers. But honestly, most days I believe less is more. I’d rather run a clean, efficient spread than have a bunch of lines in the water that aren’t producing.