So, 1740 MHash/s with the two 6990 mining bitcoin using 700W. 310 MHash/s with 7850 mining bitcoin (not only for mining purposes). I'm considering setting up another pc with 5870 and 7950 (not sure if they work together and mine litecoin).

Do you think it's worth?

For bitcoin I'll have something like:
1740 MHash/s (24/7)
310 MHash/s (10hours/day)

From the online calculators results I guess it is still worth. But probably they are not 100% accurate and don't take in consideration variables like pool fees, etc.

Could you please give me some insight? Thanks