Longer rods will cast further, are easier to work baits (jerk and glide), provise more leverage to drive big hooks home, and are easier to do a figure 8 at the boat..
8'6" is probably the most preferred length. Keep in mind they're almost exclusively one piece...in terms of transporting. There are a few with a telescopic butt section.
One of the advantages of a low profile reel like a Curado or Lexa, compared to a round reel like the Abu 7000 or Calcutta is the balance and comfort in your hand...lower centre of gravity and weight. If you're mostly trolling...no big deal...But if you're casting all day, there is a difference. Make sure you try them in your hand before buying. Many folks also prefer a single power handle (as opposed to twin paddles) for more cranking power.