I would say yes the RX is worth the extra $30 over the RS and the RX will perform quite a bit better (it's about twice as thick). But it is about twice as thick so in some instances, mounting becomes tricky.
For the tubing, I would think the Danger Den stuff would be brighter (looks to be lighter) I have some of that but haven't used it yet. I have used the primochill tubing (not the blue) and I liked it.
I would think any of those kits will outperform the H100i, the Raystorm is one of the best waterblocks currently available
Ha, I was afraid you'd get back to that. For an answer to that, I give my standard overclocking answer... No guarantees in overclocking, only you will be able to say what your MOBO/CPU/ram combo will be capable of.
Something tells me this is going to be another internally mounted build. You're watercooling to get better temps on load clock for clock (which is one of your reason maybe) then you'd best mount rad outside of case where it can draw cooler air and not draw warmer air from the case innards.
As far as tubing goes, you can pick up tubing per foot much cheaper than any e-tailer on sidewinder computers. I'd stay away from the Advanced LRT as you need to prep the system with some sort of system scrubber...which is very weird for a tubing retailer to suggest running some mystery liquid to prevent a tube from plasticizing.