If I were fishing with a 4 wgt rod and saw a 25 pound trout in the stream I would not go to the car for my 9 wgt but would cast to the lunker and if he took, I'd tough it out with him win or loose. son of a gun, IMHO thats what fishing is all about. He He He, it'll never happen but if it should, I think I could land him if the stream was slow enough!
The only change I'd make would be to use a 2x tippet.
Ol' Bill