Its certainly fun getting the fish on the lighter gear. For years I used a 30lb class rod and last year bought a 8/16 class coupled to a small lever drag multiplier and 30lb braid which has been great fun over last summer. You feel every bite and lunge of the fish and is certainly the way to go when bait fishing. Not the right gear if all you want to do is haul cod/ling out of wrecks but then I dont go fishing cos I am hungry, I go for pleasure. All the rod classes you mention will catch fish and land them but some will cope with difering conditions better than others. What really matters is you are confident using your chosen rod.
I have a trip planned for the end of may and have been recommended to bring along a carp rod , fixed spool reel and 15lb line. The target species are tope which makes this a rather unusual combination but I am told the water will only be 30 ft deep and next to no current or snags. This makes it an ideal setup for that particular weekend but a few weeks later the tackle would be no use at all!
Dave