It depends on your definition of sizable.
But, FWIW, the nature of freestoners is that they form from very small, but frequent springs. Thus, they grow gradually, and all at relatively the same rate.
Thus, the size of a freestone stream is DIRECTLY related to it's temperature profile. Smaller streams are more constant temps year round, and larger ones vary more (meaning warmer in summer).
Thus, any given area will have a "critical size", and anything larger than that is going to get too warm in the summertime, at least without some other coldwater influence like a tailwater or a large limestone trib. Anything smaller than the critical size will be suitable for, and most likely have, wild trout.
Do you think there are any sizable freestone streams or rivers that are truly productive year round wild trout fisheries?
Define sizable. They ain't all little brook trout trickles, if that's what you mean. Across the northern tier, the "critical size" is rather consistent.
Streams of that size which do produce decent wild trout fisheries include Upper Pine, upper Kettle, Upper Allegheny, Little Pine, Young Woman's, Loyalsock, and many, many others. In all those cases, as you go downstream and get bigger, you also get warmer, and lose the wild fish.
(^^^And when I say upper Pine, I mean upper, as in Galeton area and above, and with the Allegheny, we're talking above Coudersport, etc).
Most of your answers will be the bigger, famous ones like that. Smaller waters are often more productive (cause they're colder), but most of us won't name em, though as a hint, on those same streams, just go even farther upstream.
