IMO ideal flows on the big 3 are as follows:
Spring: 200ish
Penns: 300-400ish
Little J: 250-350ish
This gives you the best balance of accessibility coupled with good flows producing lots of good holding water. Also note that Spring is smaller and far easier to wade than Penns or Little J, so it can be comparatively a little higher, comparative to its size.
The max I’d try fishing them is below. At these flows, you’ll be restricted with where you can go, and you’ll need to pick your spots and not wade yourself into trouble or over your abilities, but they can still be carefully and selectively fished:
Spring: 300ish
Penns: 600-700 tops
Little J: 500-600 tops
Above these, IMO, it’s too dangerous and not worth it. Time to Brookie fish as tb mentioned.
I don’t have a good handle on BFC. Does it even have a gauge?
Kish is best at 200ish, with a max of 300 IMO.
Edit: Bottom line, use your judgement, if it looks unsafe to wade, don’t wade.