You have two very fine rods that cover quite a bit of the trout fishing spectrum; an 8'8"/#4 Scott G for moderate sized creeks and the 9'/#5 Z-Axis perfect for floating line river applications. There is little point going to an 8 1/2'/#4 like the Zenith, it is too close in size and intent to your Scott. The only 4-weight option that is logical, to me not to everyone, is a more powerful 9'/#4. I like such rods for dry fly fishing on rivers where longer but delicate presentations are required. This concept was invented by Scott's Harry Wilson in the late 70's and their S4 would be an option, the new Orvis H2 could be test cast as should the NRX #4...again, loved by me but not by many others, and I would cast the ONE too. The Circa is a very full flexing, what we used to call a, "wet fly action", rod and your G is moderate in flex so, unless you cast and loved Circa, it doesn't work with what you have. There is no such thing as an "all around" #4...a specialty line size by its low mass nature. I fish three 4's; an 8' Orvis on little creeks, the Zenith 8 1/2'/#4 on spring creeks and smaller tail waters and the afor mentioned Loomis NRX on larger rivers or side channels on breathless mornings and evenings...It generates a remarkabley slender and wrinkel free loop and will alight a trico or PMD CDC emerger exactly where I want it to land; no matter how far over the mid current the fish is rising.
