[DDCT]

Aloha,
 
I've been reading reviews here for a few years, now I am actively on the hunt for a "real" pair of phones.
 
I currently do not own any "hi-fi" gear due to lack of fundage.  
 
As a youngster I caught the audio bug, starting off with a department store 8 Track / tuner / amp system and turntable.  As a teenager I upgraded eventually to a Sony STRAV950, Cerwin Vega D9s, a Technics turntable and cassette deck, Pioneer 1st gen CD changer. My very first headphones were a set of Realistic NOVA 40, which were probably around $20.00 back then in 1982 land.  
 
As soon as I was old enough to drive I became interested in car audio,  culminating with a $25,000 / 1200 watt / 7 speaker system that placed top 5 at a USAC World Finals event in the Pro 501-1000 class.
 
My listening these days is limited to:  
320kbps mp3 files on:
a laptop playing through Logitech Z10 powered speakers,
a nearly full iPod Classic 160 through a set of Logitech / Ultimate Ears 350s, or a Sony micro system I picked up at a tag sale for $37.00, or a stock Jeep / Infinity system.
 
I've been auditioning headphones for a few weeks, with a 175 track comprehensive playlist, from 24K/SBM / DSD remasters to lo-fi punk rock, to classic Metal, to electronica, both male and female vocals including:
 
"Suyafhu Skin . .. Snapping the hollow Reed", David Torn
"San Andreas Fault", Natalie Merchant
"Herne", A Forest of Stars
"Solidify", Sheryl Crow
"Hold Me Back", AC/DC
"Xtal", Aphex Twin
"The First Taste", Fiona Apple
"Gravel Chime", Batillus
"Descending", The Black Crowes
"Duende", Bozzio / Levin / Stevens
"Cafe Reggio", Zachary Breaux
"Into My Arms", Nick Cave and the Bad Seeds
"Sean Flynn", The Clash
"Nasty", The Damned
"Blue In Green", Miles Davis
"Misanthrope", Death
"The Way Home", Devin Townsend Project
"Highway Robbery", Dillinger Escape Plan
"Eyes of the South", Down
"Trouble Every Day", Frank Zappa & Mothers of Invention
"Slateman", Godflesh
"It's So Easy", Guns and Roses
"Where Eagles Dare", Iron Maiden
"Who Knows", Hendrix / Band of Gypsies
"Into Dust", Mazzy Star
"Blackheart", Motorhead
"Sometimes", My Bloody Valentine
"Central Reservation", Beth Orton
"Cop an Attitude", Poison Idea
"Driven To Tears", The Police
"No Use in Crying", Rolling Stones
"Vital Signs", Rush
"Anymore", Savatage
"Stand Up and Be Counted", Saxon
"Problems", Sex Pistols
"Walking", Steve Tibbetts
"Freedoom", Voivod
"Volcano", Voivod
"Kentucky Avenue", Tom Waits
"Bird Out of Cage", Eberhard Weber
 
The playlist contains tracks I have heard over and over again on a multitude of home systems and high-dollar, sound quality competition car audio systems.
 
I am looking for the "sweet spot", or the "point of diminishing returns".  The best "value".  Hi-Fi in general, once you get past a certain dollar value, insanely higher prices deliver marginal improvements in performance.  
 
So far I have auditioned,
 
V-Moda Crossfade M-100 ($300)
Skullcandy Aviators ($78.00)
Skullcandy Hesh 2 ($20.00 to $60.00)
Grado SR80 ($100)
B&W P3, P5, P7 ($200 / $270 / $400)
PSB M4U2 ($400)
Sennheiser Momentum ($300)
Sennheiser HD558 ($ ?)
AKG K545 ($ ?)
Bose Quiet Comfort 25 ($300)
 
So far, there are only three clear winners:
 
Skullcandy Hesh2, great value, much better than expected sound quality in this price range
Grado SR80, amazing detail on acoustic tracks / vocals, but open back design limits use in my home
PSB M4U2, far and away the most neutral, balanced and comfortable of all the units I have listened to.

 

[Rhamnetin]

I'd say there is no definite "sweet spot", you'll get different answers from different people.  For me, after hearing the brilliance of the Stax electrostats, I feel the need to get one eventually... and I'm talking about the SR-007 ($2000) and SR-009 ($4000).  They sound much better than any other headphone I've heard.  
 
On the other hand, I've noticed a lot of people find mid-fi headphones like the Sennheiser HD 600 ($400 or a tad less) and HiFiMan HE-500 ($500) to be the point of diminishing returns, and don't feel it worthwhile to purchase higher end models then this.  Lots of folks around here don't see the value in anything better than an Objective2 amp ($130) and ODAC ($150), but users who post regularly in the Summit-Fi section will strongly disagree.  
 
To me, the sound quality difference between the Sennheiser HD 650 ($500 or a tad less) and HD 800 ($1500), both properly amped with a good source, is big.  So I suppose I'm not really in agreement with those who think mid-fi headphones are the sweet spot.  I think diminishing returns kick in when getting sources and amps valued at $2000+.  The SQ differences here aren't too drastic to my ears, compared to the SQ difference between the Objective2 amp and a quality $1000 amp which I find to be drastic.
 
It would be ideal if you get to test all sorts of headphone systems yourself, from $400 systems all the way up to $20,000 systems like I and many others have.  I suppose it depends on how serious you are about your listening.  You seem rather serious... who knows, maybe one day you'll find yourself pursuing flagship gear.