I think my current build in progress may meet the spirit of "extreme use", at least as I interpret it. My goal is a simple, lightweight, durable weapon that will be my main go-to for just about anything - classes, recreational shooting, home defense, SHTF - whatever. It's getting there, hopefully it will be shootable in a month or two as budget allows. It's a 16" midlength.

Sights: Fixed FSB and Hahn Precision folding rear.
Reason: I much prefer a fixed front for durability; I've found the Hahn Precision rear to be just about the perfect BUIS for my tastes because it has an A1 style windage adjustment (no worries about inadvertent windage changes), positive spring detents up and down, a well-designed attachment method and a very low profile - it's pretty much bombproof.

Optic: Aimpoint ML3 in a LaRue LT-150 mount.
Reason: Exceptional durability and battery life; the LaRue mount is extremely well designed and manufactured, plus it includes storage for a backup battery.

Grip: Magpul MOE.
Reason: Simple, and it fits my hand well.

Stock: Magpul ACS.
Reason: I've pretty much standardized on the ACS for most of my weapons. The cheek weld and balance are good for me, plus it appears to be extremely durable. I also like the storage compartment - at a minimum I keep a broken shell extractor tucked into mine. I'd like to see if I can find a multi-piece cleaning rod that would stow in one of the battery compartments, too.

Barrel: Daniel Defense 16" lightweight profile midlength.
Reason: Light, chrome lined, hammer forged. I've had good luck with DD barrels. I decided to go 16" over 14.5" for more flexibility down the road in muzzle devices.

Trigger: Currently RRA, but I'm considering changing to one of the Spike's coated trigger kits.
Reason: I want to stick to a milspec design, and the Spike's is getting good reviews.

Buffer/Spring: Vltor A5 receiver extension and standard buffer with a Colt rifle spring.
Reason: I'm intrigued by the reports from users of the A5 and want in. There seems to be a real benefit to the design.

Upper: Daniel Defense A4 with a BCM Gunfighter Mod 5 charging handle and BCM BCG.
Reason: Well made in spec upper; also because it came attached to my chosen barrel. (I actually bought a complete upper for once in my life.) I'm a convert to the small latch Gunfighter due to my experiences with it on one of my carbines; the BCM BCG is a gold standard component and I saw no reason to try anything different this time.

Lower: AGP Arms.
Reason: A really nicely machined, well finished lower that doesn't have cartoony rollmarks (a pet peeve of mine). Also because they will do customized engraving; I have several with custom serial number, custom caliber markings and no FA position (an issue in this silly state.)

Magazines: Magpul Maglevel PMags.
Reason: As good as it gets, inexpensive.

Lights: Surefire G2 LED in a Innovative Weapons Components MOE side mount.
Reason: Decent quality light, well designed lightweight mount that puts the light where I need it without the use of pressure switches.

Flash Hider/Comp: Micor 1N7.
Reason: I prefer closed end muzzle devices; the Micor seems to be a good balance between flash suppression, compensation (even though it's not really a comp), price and weight. This choice may change over time and is one of the reasons I finally decided to go 16" instead of 14.5'.

Handguard: MOE midlength
Reason: No need for a rail; I prefer the hand feel of the MOE.

Slinging: Boonie Packer 2P-TQA with one of the new IWC 2 to 1 Point Tri-Glides and either a Noveske QD endplate and an IWC handguard mount or a Magpul ASAP and a IWC handguard mount, still deciding.
Reason: I like my Boonie Packer slings and see no reason to change. I'm torn between mounts; at the moment, I have an ASAP mounted but may change to QD. In my opinion QD finally became an option for me with Earl's release of the 2 to 1 Point Tri-Glide, I really like being able to convert my two points to single point as needed.