Gee, this thread has taken several turns. (No surprise at that happening around here.

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Ill add a couple of comments. One thing to remember is that every rod model is different and what works well with one rod, may not work as well with another model rod. The best way to decide for sure is to go out and test cast the rod and the line.
The TiCr and the TiCrX are both very fast rods, but they are very different rods and have different tapers. The TiCr is a tip action rod, which means under tension the tip will bend first and as line tension increases the rod will start bending further down. I cant remember the correct technical term, but the X is designed to bend deeper down the rod quicker when tension is applied. The TiCr is technically a faster action rod than the TiCrX, but the X feels faster than the TiCr to me when I have cast them side by side.
For my casting style, the softer tip on the TiCr means that I can load that rod at shorter distances without needing to upline. I do not like the way the TiCr casts when it is uplined, but that is my opinion, and Ive met other casters who love the TiCr when it is uplined.
I think the X casts very well when uplined and it seems to handle uplining one or even two sizes just fine. I would expect the 6 wt TiCrX and the 7 wt Sharkskin line should be a good combination.
The Axiom is my personal favorite of the three. The casting action feels slower than the TiCr or the X, but it seems to have the widest range of line sizes that it casts well. That rod casts its rated line wt well and it can be uplined several sizes without noticeable impact to how it casts. My daughter has a 6 wt with a 7 wt SA MED line that I would like to steal from her.
Someone mentioned the GPX lines and they made a good point, the GPX lines are a half size heavy. So, the 5 wt line is actually a 5.5 wt line. As mentioned, if you put a 6 wt GPX line on a 5 wt rod, you have actually uplined 1.5 sizes. The GPX style lines are popular since they provide an option to split the difference and just upline half a size.
Have fun,
Rex