will fit thicker GPU say 2.5 slots or perhaps even 3 slots if not for IO shield limitation.
and no, you can spread the USB cables apart that you dont have to remove/mod the cables but doing so does stress the cable.
by maximum length i mean the card literally presses against the aluminium front panel(will need some slight force to push the panel so the screws line up) but somewhat still clears the power button and USB cables.
if you really have to use such a long card then so be it but i recommend against it
note that the 670 DCUII has the cooler shroud overhanging the PCB which kinda allows for some compression while the 770DCU's PCB is longer then the cooler.
IMO the case itself is fairly silent to me and top fan is great to have but not entirely necessary. just by having a hole up to made all the difference. my top 140mm fan doesnt need to spin even on a hot summer day to keep the temps comfortable