I'm using the xspc v3 as it is a very unrestrictive block and suits the rest of my system since I have the gpu and nb on the same loop as the cpu.
Not sure it is worth changing yours as I have always stated in this forum, your whole watercooling system needs to be matched. However, the xspc v3 is a much better block than the fuzion v1 but not as good as the fuzion v2. You might see a degree of two of change. If that is going to get you a better overclock then please feel free to swap. If not, I'd keep what you have already.
My point to the op though, is he is looking at spending £14 plus postage just to use the block on his i7 so it's worth changing his to a better block for little or no money.