Re: 8.5 or 9 ft for a 4wt?
Besides the environment to be fished, it really depends on the design of the rod. My antique Orvis 8'/#4 Western as never needed to be replaced because it is just a small stream special with its little CFO IV. I love 8 1/2'/#4's for spring creek dry fly fishing and recently added a new (but older tech) one to my quiver. It is a Loomis Streamdance GLX and a delight to fish...if I could only have one #4 this might be it. However, I have more rods and I have commented before how spectacular the Loomis NRX 9'/#4 is...but it is NOT a small stream rod. This is a 4-weight for bigger water and it features low end grunt with a highly responsive tip that encourages me to use it instead of a #5 (but with a straight RIO Gold #4 line) on big dry fly tailwaters and the Fork. So, the answer is, it depends.