Do not use RG58U, loss is very significant on 460MHz. Just look at what Lscott listed. Another reputable company that sells cables with connectors is dxengineering.com They have 25', 50', 75' runs of their LMR400 equivalent with with N-connector or PL259. Coax loss charts: https://w4rp.com/ref/coax.html If radio-cable-antenna-connectors system is well-matched through all the components, the length of the coax will not matter. The 1/2 wavelength cable allows you to tune your device (usually antenna) more precisely with some equipment. Once match achieved, coax can be any fraction of wavelength. So, don't worry about it unless you plan to invest into instruments and knowledge. And 1/2 wavelength on GMRS is roughly 325mm, so quarter-inch less or quarter-inch more and you are out of optimal length anyway. Velocity factor is also needed to be considered... Do not worry about coax length. The shorter the better, but that's it.