I think as it stands right now most people are going to be better off with the Q701 and adding the K712 Pro pads for $70. In the end you save $130 and end up with a headphone darn close to the K712 Pro sans the headband and some slight midrange smoothness.

If you get a chance, try the Annie too. I bet you'd find it slightly worse! I read every word of your review and trying to test some tracks for fun. I was listening to that Maroon 5 song and it sounded best on the HD-650. The vocals didn't feel forward at all on my Q701 or HD-598, but on the Q701 it was a bit thinner/trebly. Strangely on the Q701 + Annie pads it was harsh and had the most forward sound. Even less bass presence than my HD-650 which is weird.
The hard part is figuring out how the recording was SUPPOSED to sound. My HD-650 just seems to be adding some nice coloration and making my ears prefer that type of sound. You should hear that track on the K400. Very thin and tinny sounding. It'd be interesting to hear it on something like the KRK KNS-8400 or SRH-940.
My Q701 always sounds smooth in the mid-range unless it's a crappy recording. That's also when it's treble bothers me. For example I can't even listen to any Sigur Ros stuff due to the harshness on some tracks. When I don't want to be bothered by that they're a little easier on the ears on my HD-650. The 598 has smooth treble to my ears also.
You know what's weird about my Q701 is some songs sound very full and warm sounding like an HD-650 and other tracks are tinny/harsh like an AD700. Totally bizarre. Some bright Jpop is unlistenable on the Q701 almost. I can't really blame the Q701 for that though. Try the Buena Vista Social Club CD on the Q701 if you can. Sounds perfect on the Q701 and better than even the HD-650.
Someday i'll try a K712. Who knows..maybe i'll like it more than the Q701. I'm not really a fan of the Q701 + Annie pads but love the HD-650.

I understand where you are coming from and having all three headphones ( HD650, Q701, and K712 Pro ) at hand makes me realize that each has its own perks and drawbacks. Each headphone I would keep in its own right and would recommend each one.

Thanks for the review. Some classical/orchestral examples would have been welcome seeing as this series of headphones is usually touted as good headphone for classical music.
As an aside, I've noticed that the word "tad" is increasingly one of the favorite words in headphone reviews these days. A "tad" too much this or just a "tad" too little of that. There are nine or ten "tads" in this review alone. I'm thinking of launching a campaign to banish this word.

Thanks for the comments wrightanswer. I made some changes to the review and plan on adding in some orchestral review. Any particular piece I should listen to? The issue I have with orchestral is most of what I like tends to be from older recordings and is not mastered perfectly thus biasing the review of the headphone.

It would be nice to have some smaller scale classical, like a string quartet or trio, which would be recorded relatively closely, as well as orchestral with a "tad" more expansiveness.

Added classical listening September 3rd 2013.

Well done. Thanks.

Great comprehensive review.  I was a bit unclear if you drove it directly out of the iPod ("in further listening" paragraph) or meant that you used the Ipod just as a source? 

Updated the Gear section to properly describe how I did the testing.

I kept my ratings honest and only justify 5 stars for a perfect headphone.  To me the K712 Pro is as perfect as I have heard next to the STAX SR-009 driven by the Blue Hawaii amp.
 
This rating may place it at 171st place here at Head-Fi, but it outclasses and outperforms many other headphones rated well above it.

Anyone heard these (or the 702) via the Apogee Duet 2 (32 Ohms output impedance)? 

Corrected some wording regarding the Q701 September 16th 2013

 What an awesome review, thanks!  Comprehensive and very helpful.  Given the difference in price in the US (double!), and the 'slight' improvements noted on most of your tests, I'll go with the Q701 (as an improvement to my K702) and wait it out until I can afford the T1.  I'm sure I'll be thrilled with it.  And if and when the K712 goes way down in price, and is available used, I may upgrade at that time by selling my Qs.

 I find my K712 to be just flat out great (with Bifrost Uber, Lyr, and Asgard II). They are better than my Q701 and the comfort is tops. Very happy with 712.

I keep waiting for professionals like Tyll and HeadRoom to conduct their reviews because I find the AKG K712 Pro quite competitive in the HD800 market.

It remains the most speaker-like headphone I have heard to date.

Wish I could afford this! When they come down in price to $300 or so I will buy a pair and do the bass port mod on them. I'll then compare it to the modded Q701 and see which one I like the most. Who knows..maybe i'll actually love the K712 despite not liking the Annie much.
 
I hope Tyll can do a K712 vs modded Q701 comparison. Probably no chance of that happening but it'd be nice to see measurements of both.

Modded Q701?  I must've missed this.  Can someone please fill me in on what the mod is, what issues it solves or improves, and where to get it?
 
To this day, the modded D2000 I had from Mark Lawton was one of the very best sounding headphones I've ever had the privilege of owning.  Solved all the problems of the D2000, including the one mentioned in this review (bleeding, flappy bass).

September 26th:  Added a HE-500 comparison

Brilliant review, thank you, i have just ordered them!