Good points - thank you!
Does it matter that the Crucial RAM I specified is not XMP ready? Will that make overclocking more tricky? (Never overclocked before.)
As for the MSI 980Ti + Noctua NH-D15S + ASRock X99 Extreme6 combo, do you really think it could be a potential problem? The backplate only seems about 3-4mm higher than the actual PCI slot, and the D15S extends downwards 67mm (apparently) from the centre of the CPU. I suppose I could contact ASRock and ask them what's the distance between the centre of the CPU and the top PCIe slot, but up until you mentioned it I never even thought this might be a problem.
Thanks