I have landed one rainbow that looked about like that, and he weighed 17.6 lbs. He was way more orange and red with a dark green back and a hooked jaw. I caught and released him in the Colorado river in late January, with ice blocks the size of VWs floating down the river. Took about 20 minutes to land. Probably would have taken twice that long in warmer water. I have hooked ones even bigger than that but they go bye bye about as fast as an ice cube in the oven. The Colorado River and the Gunnison River in the Gunnison Gorge have Rainbows like this and some browns too.
Tyler