[Lumos]

Disclaimer: This is my purely subjective opinions: My music, my gear, my ears. Please take it all with a grain of salt - especially if it does not match your own experience.
 
Gear: Schiit Magni/Modi Asus xonar X3 as DAC
Recordings I take as reference:
  The Vivaldi edition naive recordings:
vol 3. Concerti per fagotto e oboe (Sonatori de la Giosiosa Marca) (2004)
vol 5. Concerti per fagotto I [Sergio Azzolini, L'Aura Soave Cremona] (2010)
Vol 1. Concerti per flauto traversiere [Kuijken, Academia Montis Regalis] (2002)
Vol 1. - Stabat Mater, Concerti sacri (Alessandrini, Mingardo) – 2002
 
Amber Rubarth (2012) Sessions From The 17th Ward (Binaural) (24-96)
2004 - Marantz Hi-End Audiophile Test Demo SACD (7th Edtion)
Art Blakey and the Jazz Messengers - Moanin' (1958) {VINYL} [Ltd Audiophile Japan -TOJJ-6503 180g LP) [24_96]
Hector Berlioz, - Symphonie Fantastique (Ansermet OSR)
Tiger Lilles 1998 - Low Life Lullabies [FLAC]
 
When I first listened T1 I thought, it was much more ,,liver'' sounding phone with twice larger soundstage and ,,quicker'' bass. Since that my impressions are not changed much. Now comparing side by side 650 and T1, it is like comparing live concert and very good studio recording. However, more I listen both headphones more I am revealing some flaws which are described below.
 
Here is the raw frequency response graph:

 
As you see the major difference is 8-10 Khz and 12-14 Khz. Probably this makes Beyer much more bright headphone. But it is not a full story. T1 has a way better puncier/texrured bass, 300 Hz Square Wave measurements exhibit some ringing and treble could be little hot for some music.
 
HD650 is very smooth sounding very well detailed phone. I should repeat here as many people said before for my ears they are extremely clear and not veiled. Rather I would use words: never being sibilant, little not exiting.
 
I like T1 because of :

1. Very deep punchy Bass without much D2 distortion
2. soundstage size and deepness

 
Things I don't like with T1 are:

1. Treble could be a little hot for some (depends gear music and taste)
2. Price
3. Beyerdinamict quality control issues

 
I like HD650 because of:

1. Never being sibilant
2. better bass then HD558/598
3. decent soundstage size

 
Things I don't like with 650 are:

1. D2 {6-10%} distortion and this is big issue with 650 and very easily pickable when compared to T1. For measurements please visit innerfidelity.com

 

[GaryPham]

Very interested in any future updates you have on this.  I also own a paid of HD650s and enjoy them very much, but was blown away when I heard the T1 at a recent head-fi meet.  As we all know, the world of head-fi is quite a money pit, and although I told myself that my HD650s were going to be my "end game", right now my top choice if I ever chose to upgrade would be the T1.  My experiences with the T1 were only a mere 5 minutes of test listening on a Bifrost/Valhalla combo, but to my ears they were amazing.  I'm curious to see your long term impressions to decide if the T1 is worth the upgrade over the 650s.

 

[Lumos]

deleted sorry