This remains a cue (to me), Matt, that your back angle is still a little flat at the start of the pull and perhaps accounting for the discomfort -- your neck is not neutral in most of those reps. With just a little more incline in the back angle, you'll be looking a little farther out and maintaining a neutral neck position. Ideally you'll be looking out about 8-10ft in front of you.
I agree (with Spar and Mike) that your legs are longer than average, accounting somewhat for the flatter back angle. I was also re-watching Ripp's SS DL video on anatomy and set-up etc., and the "long legged" guy example they use still seems to show a slightly steeper back angle than you're getting here. That said, he also has long arms compared to yourself, and the angle of the camera sucks.
The relevant info is in the opening minute... but listen for the "back on your heels" cue around 52s and pause.
That's where I am saying your back angle could do with a little more steepness... I agree my original 4-6" is likely off at this point, but 2" would be just about right. Between a combination of "squeeze the chest up" and "back on the heels" cues, you may find your butt naturally drops the 2" I'm describing.
http://youtu.be/sP4FwBkuK6o
Anyway ... I think Spar hit the nail on the head when asking "How does the pull feel to you?". You'll have to feel this out for yourself and update the thread with feedback.
Try playing with some subtle adjustments to the back angle, including the advice of locking in the back and maintaining extension throughout each rep across the set... you will almost certainly feel stronger when you hit the sweet spot.