I would go DT880 or 990 for the Beyer's. The 770's arent nearly as flat I believe due to them being closed back. I've used 990s and I liked them a lot.
I personally have Sennheiser HD600's and they're a little more money, but the detail in them is spectacular. The stereo imaging is fantastic, and they are super comfortable. They're not too heavy, and they fix perfectly on my ears.
Only downside is that they kind of taper off at 30-40hz, so you don't get the best representation of sub bass, but I typically just check that freq. range out with something else, just to double check how it sounds down there.
The only headphones that I've heard are flatter are the HD800s (Double the price) and my friend's Audezes, but those are $2000.