We've all had moments like that.
I once noticed after a whole days salmon fishing, with the spey line flying out effortlessly, that I had the tip section from another rod on.
Not just that, but one rod was a 15' Daiwa Wilderness #11 which is like a telegraph pole, and the other rod was the 13' Greys GRXi which is like a whippy fairy wand.
I never noticed the difference in my casting, if anything I enjoyed the whole day with effortless casting.
What line are you thinking of purchasing for your salmon fishing then Andy?