We can speculate on the Mac Pro, but none of us can make a proper judgement until Dec when we can view the customization features.
Now most video editing software will use the GPU to boost rendering. You could make a better judgement call buy reviewing the specifications of Adobe Premier or what ever video editing software you will be using. Things to look for, does it use the GPU, how many GPUs can it use at a given time. How much of the software will take advantage of the GPU acceleration.
Then there is also the space requirement for video and audio editing. 256GB isn't going to cut it. This means your going to need external storage. Most NAS and USB 2 drives will limit you to 30MB/s. Trust me even iTuns lags on a NAS reading music. This means your gonna have to look at a Thunderbolt attached storage and preferably a RAID one. They are very very pricey..
Now the Xeon offers much much more on die Cache over the i7. The ECC RAM support is marginal for most workstations IMHO. But if your data is critical then this is your best option.
After looking over the Mac Pro specs the past couple of weeks, I have decided that its a contradiction in its self. The system screens 3D modeling and video editing. Yet they have stuck you with a 256GB flash drive?!?!!?!!? WTH here! But like I mentioned, we don't know the final specs yet.
Now I for one love the look, don't mind the Xeon as its fast, I even like the Fire Pro 300. Which turns out isn't bad for gaming. But would love it if Apple will offer the option to drop one of the video cards in place for a 2 or 3TB 7200RPM 2.5" drive. If they would, I would start kissing up to the wife today to get one. But I don't need 2 video cards, Lr doesn't use them anyway and I need storage space for photo editing.