I really depends on the stream.
For a few I know of, it should make a good difference.
For most, you wont see a difference. That is provided they aren't unstocked streams that get fished hard in the beginning of the season, in that case, you may see a difference. (You have noted that trend in the past and I have witnessed it myself on First Day.) In those streams the difference would be more 7" fish than you see now but you wont see more 10" fish.
I still believe this is a good move, but be careful. Its more likely to benefit our wild brown trout population over our wild brook trout population.
Wild brown trout growth in Pennsylvania typically reaches 7.0 to 8.5 inches by the end of their second growing season.
- Second Year (Age II): Studies of wild populations in PA show average total lengths of 7.0 to 8.5 inches after two complete growing seasons.
- Sexual Maturity: Most wild brown trout reach maturity in 2 to 3 years, ready to spawn in the fall (late October through December).
This means you could have a lot more sexually mature brown trout reaching the spawning areas than you do in some of the streams now, because they cant be harvested until the 3rd season (likely in the late spring they will reach 9") In streams with a mixed population, it could be the final nail in the coffin for brook trout.