1. If you're going to be doing anything above low end overclocking (around 4.0GHz or higher), an aftermarket cooler is highly recommended and pretty much required. Aftermarket coolers are nice to have even when not overclocking just to keep the system running cooler under load and because in my experience, the bundled Intel cooler can get quiet loud.
2. It varies due to different manufacturers and socket types having different mounting systems. I don't find the Cooler Master Hyper 212 Plus/Evo to be very difficult, but some first time builders here say it was very difficult. Generally for air coolers it's easier to install either the backplate or the entire air cooler before placing the motherboard in the case, then I just lower the motherboard into the case and secure it. Water coolers are easier to install when the motherboard is already in the case, I feel.
Custom loop water cooling is an entirely different beast, that requires DIY knowhow, some design thought, and plumbing, as well as costing a hefty premium.
3. Varies from
test to
test to
test. The best possible AIOwater coolers that cost around $130 seem to generally beat out the best possible air coolers that cost around $100 by a few or couple of degrees, but if I were to consider options at the same price level, I'd usually lean toward air coolers.
Water coolers will rarely ever beat or match air coolers in terms of price-to-performance, that much is certain.
4. Doesn't apply to sealed, pre-assembled water cooling kits, no idea about custom loop coolers.
