Well after a little over 4 months with the LCD-2f and a Fiio A5, and lots of reading on head-fi, took the plunge and upgraded to the LCD-4. I listened to almost everything higher end available at NYC CanJam (Utopia, HifiMan, Stax, Abyss, Sony, LCD-X, LCD-3, and I own Grado RS-2) and did A/B testing with music I know well against my LCD-2f. Whenever possible (and most of the vendors were exceptionally accommodating) I listened to recordings of classical pieces I've heard live using my iPhone 6s running Spotify Premium (have since switched to Tidal; thank you head-fi) and the LCD-4 just sounded the most accurate. I only listen to my headphones on the road so I paired them with iFi micro idsd black and, from memory, suspect I'm getting about 80% of what I heard the LCD-4 give me through the highest-end Schitt at CanJam (probably the Ragnarok; sorry didn't take notes. Maybe someone who attended the show remembers?).
Adorama's salesguy, Alex, ordered the LCD-4 from the warehouse just so I could A/B test them against my LCD-2f and Fiio setup. Through the Fiio I could not really justify the purchase because the perceived differences were so slight. So Alex brought me the ifi and then it was night and day. The LCD-2f also sounded better through the ifi, though I didn't spend too much time identifying the actual benefits since by that point I'd already decided. The A5 seemed maybe to be running out of gas on more complex passages. By the way, I thing the A5 is an excellent amp for its size and greatly improved my LCD-2f over the 6s. I bought the amp after auditioning Fiio at CanJam. I did try the Dragonfly Red before the Fiio and it just wasn't enough for the LCD-2f.
In general, I'd stopped listening to large orchestra classical pieces on headphones or rather I never did. I found the sound offensive to my memory of the pieces but today I spent the day with Neville Mariner's excellent Mozart Requiem and loved it. As I've intimated, I audition equipment with classical pieces I've heard live but the LCD-4 makes every song I'm familiar with sound better (to the limits of the recording). Even my guiltiest pleasure, Selena Gomez, sounds like she has some range beyond the production magic on her Bad Liar.
Mind you, I'm only using the ifi as an amp (I'm trying to keep things simple) so I don't know what it sounds like through the dac. Maybe someone can comment on whether the iphone 6s dac measures significantly flawed.
Now, if only ifi came up with an amp only slimmer, more powerful amp, I'd be fully realized hobbyist.
By the way, for those who haven't heard it the Shure 1540 challenge the LCD2f at half the price.