Its 6GB total but really only 3GB per 7970 core which is quite handy for eyefinity. Still the price is likely to be Ares II level so not really practical even for those who do have an actual "need" for this level.
Only display port? No go for me with 30" monitors that need dual link DVI. The active adapters are $100 and last only a few months before dying.
What active adapters are you using? The active adapters I got for my Crossfire HD 7950 and Crossfire HD 7970 setup only set me back $30 and have lasted for over 2 years. Got them back when I got my Crossfire HD 6950 setup and I am still using them on two different rigs.