Well i don't know where in the world you are but im in the UK and a 6850 can be had for about £120, possibly cheaper i just took a quick look on Ebuyer and that was the first price that came up.
A 6850 will run games at about the same level as two 4770's , you wont have to worry about driver profiles for games which you have a good chance of not properly supporting the card anymore anyway.
Personally i would buy a card like teh 6850 or even a little better if you can afford it then either keep the 4770 as a spare or sell it to offset the cost.
End result would be a single card that will perform about teh same as dual 4770's no Crossfire issues and if you sell the 4770 on then its cost about the same as the second 4770.
Also you then have a card thats worth selling on again in a year or so to of set another upgrade and not 2 obsolete cards that are worth little.
Win Win as i see it