Ahhhhhh! You guys are killing me here!
Talking about rod tapers is not exclusive of the "tip". The taper of the rod is the rod as a whole. You canno have a moderate rod with a fast tip, and you can't have an XFAST rod with a moderate tip. It isn't possible. To introduce a parabolic bend in a rod is specific to the parameter of the entire blank- you cannot have a parabolic "tip." It isn't semantics, it IS the physics of rods. Period. A parabola is defined as a symmetrical open plane curve- any point on a parabola is equidistant from a fixed point at the conical entrance to the directrix. You cannot have a parabolic bend in the "tip" of a rod. You just can't.
Jerkbaits are best fished on a fast or extra fast rod. The reason being is that you need the rod to move the bait, move to recovery or neutral position, and load as rapidly as possible. A slower rod will not do this effectively. You generally are also after a reasonably powerful butt section in a jerkbait rod, which effectively means that you are after something less flexible. This leads to a fast or extra fast taper- the tip of the rod has nothing to do with it.
Look at it this way- the speed of the rod can also be looked at in how rapidly the blank returns to a state of potential energy. As a rod bends more progressively, it is going to take longer to return to rest IE: a slower taper. It is not the power of the rod. The same is true of a rod that does not bend as far down the blank, which is where the misnomer of tip action comes from. When a rod bends only in the very tip section, it is very fast generally. That same rod will also take much less time to return to rest than it's more moderate counterpart.
As previously mentioned, fast or XF rods are more desirable for jerkbaits because of how you want to move the bait. There are exceptions to the rule, but most anglers- myself generally included- cannot effectively control a bait with a rod that is too slow. The second aspect of that, is that you are generally unable to feel the subtle takes with a slower rod.
When it comes to jerbait rods I would be happy, and am happy, to spend as much on them as I do my jig rods. Essentially, that's what I am looking for, really. I want a rod that is super sensitive, ultra quick in hand as well as in taper, and I want it to respond to everything. The same qualities I look for in a jig rod, albeit in a shorter package.
When it comes to length in jerkbait rods, I'm a very firm believer in shorter is better. I've only met one person in my entire life that can effectively fish a 7-0 rod for jerkbaits; and he's 6-10. Too long a rod and you're slapping the gunnel, the water, or you're sweeping the rod too far. I fish a 7-0 for one style of jerkbait, however it's a bait that I work with the reel, not the rod. Optimal length for the average person is something between 6-3 and 6-6. I fish more modified 6-8 rods than anything. They start as 6-8 rods that I have trimmed the butt and handle and refinished. In doing so, I've allowed a handle length that I can still utilize effectively without getting it caught on clothes or my arms, and I still have enough leverage.
Sorry for the rant- but I see this come up so often that I can't always hold it in. Look in the jerkbait thread for really good info, as well. Search this forum for jerkbait rod threads, too. There was one somewhat recently that is superb for the information in contains. There are a couple or elite series pros that chimed in on that one, and I think an unnamed rod designer as well.