I own both the Spirit Pro and DT1350 and did a ~30 min listening session with both of the headphones. Here's some impressions on both.
I used mostly metal by Eluveitie and Edguy to determine how the speed/attack factor is between the two. I'd say the attack factor is mostly even but it's probably a little bit more apparent with the DT1350 thanks to the more emphasized treble. I doubt there's any actual difference in it though. The most apparent difference between the headphones is basically more sub bass on the Focals while the DT1350 pushes more bass onto the mid/upper bass region. Regarding detail I'd say that the DT1350 in this aspect blurs some of the mids more than the Focals, so the Spirit Pro wins on the detail side with louder music.
I tried some classical music for the detail/dynamics side. Sort of same line of thought here. Every little detail is there pretty much similarily on both headphones, but I have to press the DT1350 more against my ears to hear the low notes as clearly as with the Focals. Midrange and treble are pretty much on-par detail-wise. The DT1350's treble peak at around ~9kHz is a little bit annoying with trumpets and such, although generally its sound signature fits better for classical than the Focals do IMO.
tl,dr: Sofastreamer's assessment is pretty good. Detail-wise both are pretty much on-par. Focal has a more evenly spread dark sound signature while the DT1350, while still fairly neutral, does have a noticeable bump at mid bass and that treble peak. The lack of significant frequency peaks is pretty much the forte of Focals detail-wise, but the dark sound signature does make the treble region a bit recessed (although not blurred).
Edit:
Regarding the Focal Spirit Classic I did only a short listening session between the two when getting the Spirit Pros. I couldn't perceive audible differences in their sound. The Classic just looks better and has a better cable for (living room centric) home use.
