Puttin together a new machine soon and I really can't decide what I want for cooling. Going with I7-5820K and Fractal R4 case.
I'd like to OC the chip to at least 4Ghz. I need cooling that is virtually maintenance free and long lasting, this is why I'm skeptical about water cooling. The Arctic 7 Freezer I've had on my current machine for the past 7 years or so has required nothing but the occasional air blast from a compressor. Can the same be said about Corsair H100/ H80 series? My PC serves many purposes: work, gaming, movies/TV and will be on 24x7 so I can't afford much downtime. 
So air or water and which cooler would you recommend? Thanks.
		
		
	 
That case may work with an H80, but I'm not so sure about an H100.  
  
 You might want to look at two fairly current threads:  WGusler's thread on his C70 case "ammo box" project and an H80, and a thread started by Lepton87 about cooling the 5820K.
  
 The 5820K has a spec TDP of 140W, compared to WGusler's i7-4790K of 88W.  Lepton shows some results using a Noctua NH_D14 cooler, before choosing to get an external radiator for water-cooling.  And I think he shows some results overclocking to the level you seek, but I would look more carefully at his posts so as not to rely on my own memory of it.
  
 This is a problem that I, too, have given attention.  And I plan to give it some attention into the middle of 2015.  My choice is a bigger case than the Fractal, either a "fat" single-fan "square" radiator or 40mm+ thick dual-fan radiator, with a dual-pump bay reservoir.
  
 I have this EVGA ACX heatpipe-tower which beats my D14 hands-down by about 5C degrees with a careful choice of fans and minor low-tech enhancement for both test coolers.  I just don't think it's enough for overclocking a 5820K -- or not for the way I'd like to overclock it.
  
 The AiO coolers have evolved to greater reliability.  Some of them have A-grade water-blocks and pumps.   But they only come configured with a single pump, and a pump may last a few years.
  
 A Noctua NH-D14 can be made to match an H110 double-fan AiO cooler in performance.  
  
 Personally, I think any "serious" overclocking of a 5820K needs more radiator capacity than an H110.  Right now, the attention is on a Swiftech H240X cooler, which arrives as an "AiO" cooler but has fittings for expansion -- making it potentially "custom-water." 
  
 
http://www.techpowerup.com/reviews/Swiftech/H240-X/
  
 And I don't think that cooler is going to fit in the Fractal case.