Performance
There isn't a great amount separating the high-end coolers in terms of CPU temperature, with all four non-reference solutions showing a massive improvement over the default Intel cooler.
All three liquid coolers have a slight lead over Noctua's NH-D15, with Corsair's Hydro Series H100i GTX delivering the lowest actual temperature. There's little in it, mind, and neither option has any real difficulty in taming an overclocked Core i7-4770K processor.
With performance closely matched, today's best coolers are better differentiated through other key factors such as easy of use, aesthetics and noise level.
When evaluating the latter, Noctua's NH-D15 is noticeably quieter than all of the liquid coolers on show, and if you like your PCs to run quiet, you will notice the difference. Our noise readings suggest that Corsair's H100i GTX is one of the quieter liquid coolers, but we feel the numbers in this case don't paint an entirely accurate picture, as the Hydro Series pump seemed noisier than our noise meter is letting on.
A quick online search reveals that pump noise is proving problematic, and this is irrespective of whether it's run using the quiet or performance profiles available in the Link software. The H100i GTX is too vocal for our own personal liking, and with our quiet test platform touting solid-state storage and a graphics card whose fans turn off at idle, the addition of a 2,800rpm pump feels counterproductive.
