Crossfire on x16 x4 takes a performance hit and is not recommended although it will work just will not give the same gain as x8 x8 or x16 x16.
Thank you for the reply.
I checked some other cards' specs for similar performances, and it seems that the best alternative would be to sell my current 5770 and upgrade to a single 5870. The 5870 offers roughly the same performances as a 5770 CrossFire setup. For about the same price as if I was to buy 2 5770.
I wish to stick to ATI cards, because of their low energy usage, price and how silent they are compared to NVidia's.
If you know of a better alternative, please do tell.