Here's a video review of 750D,
link:
https://www.youtube.com/watch?v=ZpoQqdeqnTo
And the specs page too,
link:
http://www.corsair.com/en/obsidian-series-750d-airflow-edition-full-tower-atx-case
From cable management standpoint, there's not much difference between the two cases. You got plenty of space behind MoBo tray with lots of tie down points in both cases. Rubberized cable routing holes are standard for high-end Corsair cases.
As far as cooling goes, i'd say 780T is better choice. Mostly due to it's built-in 3 speed fan controller that can support up to 5 fans.
Most MoBos only have 3 case fan connectors on them. When you have more than 3 case fans, you either have to use Y-splitter (to connect 2 fans to one MoBo connector) or use fan hub/controller.
If you mount all the fans in 750D, depending on the fan size you use (120 or 140mm) total amount of case fans would be either 7 or 8. Without built-in fan controller and only 3 case fan connectors on MoBo, you're left with 4 to 5 fans that needs to be connected somewhere.
No such problem on 780T. Fan controller houses 5 fans leaving 3 to be connected to the MoBo. Depending on fan size you use, total fans in 780T would be either 7 or 9.
780T also has a little better fan filtering built in. While 750D has only PSU fan filter, leaving the 2x 120mm bottom fans without a filter, 780T has the entire bottom of the case filtered.
Both cases also have top and front filters.
While 760D in front supports only 2x 120/140mm fans, 780T in front supports either 3x 120mm or 2x 140mm. 780T also allows you to set the height of your rear 120/140mm fan. No such luxury on 750D. 120/140mm fan mounts are fixed in place in 750D.
Also, there are plenty of space around GPU in both cases.
If you like the standard looks of 750D more than curvy looks of 780T, go with 750D. And vice-versa. It's pointless to have a case just because of the features it has while you dislike it's looks.