When fishing streamers for trout, I use the 20% Rule and avoid throwing them at high noon.
Some of that comes from Jason Randall, who wrote this great book on why and how trout feed. He believes most trout will try and eat prey that are 20% of their length or less. They know that successfully attacking and consuming something bigger has lower odds. And, trout are all about maximizing calories eaten vs. calories expended.
I do so because most of the trout feeding during the day are that size. That is because big trout cannot get enough calories from consuming bugs. They need to feed on other fish. And, those smaller fish are easier to ambush at night.
What if you want to find big trout with a streamer when it isn’t spawning season? I would target dawn, dusk, or night.
Big fish leave their resting lies around dusk and begin the hunt. Those lies are usually around log jams in the water. You can catch them there as they start their work day. Those same fish prowl around at night, and some of them journey over two miles in an evening to find prey. Then, they return to their resting areas just before dawn, and you might be able to catch them then.
Of course, sometimes rules are meant to be broken, and that’s why fly fishing is challenging. If a lot of rain starts, or if there’s a major bug hatch, big trout will throw caution to wind.
If you’re going for big spawning autumn Browns, of course, throw something larger. But, know that those fish are reacting to defend their territory vs. trying to eat prey.