A few comments, several of which have already been made, but to emphasize:
70-80ft with a short head like a Rage is very reasonable, and, will cover many if not most practical fishing situations in my neck of the woods. From watching a lot of casters, my observation is, with that type of setup, 80ft is about the maximum consistent distance for most casters, probably less by my definition of 'consistent' which would be : 85% + of casts straight and fully turning over, off either shoulder, on both sides of the river.
Most people over-estimate how far they actually cast. Go try it. Get a friend and mark out distances on a pond, have the friend spot five or ten of your casts, compare to your estimates. You may think you know your distance from adding running line + rod + line + leader, but, you'll be surprised how much distance you lose from slack, from casts that are not quite turned over, and from casts that are not perfectly straight. So don't believe what you read on the internet about how far other people are casting. Every so often we'll get someone on here that claims to be casting 120ft with a six-weight switch rod and a short skagit after a month of solo practice. Not very likely.
You want to add distance, my advice would be, #1, find a good instructor. At every level of expertise, the most important thing is attention to the fundamentals of casting. Everything else is secondary. I've been doing this ten years now, have had the great privilege of learning at the knees of some of the best, I still don't fully have the fundamentals down. Most people, past a certain point, will benefit greatly from external input. Videos and solo practice will only get you so far.
#2. Yes, if you want to reach over 100' consistently, going to a longer head is going to help. That is partly due to equipment. What hasn't been mentioned is longer heads are going to be more revealing of casting faults, faults you may not have realized you had. It is a way to encourage your skill level up. Now see #1.
#3, And, also, yes, changing your running line can give you more potential distance, at some point it's a must, but from where you are IMO it is a distant #3. No reason not to experiment with it, but don't fall into the trap of chasing equipment fixes to technique deficiencies.