Thank you, ultimately the decision on that came down to aesthetics. I love the look of the heatsink and fan dominating the motherboard, after all the build is pretty centered around the Noctua iPPC theme. Adding a CPU block would of made the loop appear far more complex and perhaps made it feel slightly emptier. Naturally it would of also added significant heat load to the loop which was only ever going to be big enough for a single 120mm radiator. What more can I say, I like big heatsinks and blocked cards!
So far the cooling performance observed has validated my original thinking. This was rather crude testing and I will endeavor to provide some more controlled and accurate results over the coming weeks but the highest temps i've seen on the GPU so far are 52°C and similarly 51°C on the CPU and that was running passively without a fan on the CPU heatsink after 8 hours of gaming.
I should say as well this really isn't an overclocking or benchmarking rig, it's running a locked multiplier i5. I've got other toys for that kinda fun, this one just had to be pretty and hold it's own while gaming.