It still pays to use better coax if you can. 27Mc is close enough to the typical 30Mc db loss figures to be considered the same, 9913, lmr400, and even cable tv coax would do better than most rg8 and rg58. Better coax helps out on tx too, if all you have is 12w of ssb power from your cb, better coax will help get more of those 12w out the pipe.