If you Crossfire with a 1gig card you will only be able to use 1gig as both cards will on use the lower amount.
I have a Crossfire HD 7950 and a Crossfire 7970 based rig and so far have not had any problems at all with Crossfire. I have read about the latency issues but have not had any problems with any of my games, over 300. Before the 7950 and 7970 cards I had a Crossfire HD 6950 setup and did not have any problems with that ether. Maybe I have just been lucky.
I think when they say latency they are talking about the amount of milliseconds per frame. I guess crossfire has a much higher amount of ms per frame than NVidia sli has, but it's not always noticeable. If you have a high enough ms per frame count, it defeats the purpose of having high FPS, because it doesn't run as smooth as it should.