valley does not seem to favor the new hawaii chips for some reason. as far as gk104 vs tahiti... their both right in line as far as benchmark numbers with the full tahiti chips in the 7970/280x generally beating out the gk104 in the 680/770 by a small margin with high overclocks. the gk110 hold a huge lead over the hawaii chip, especially after overclocks.
my single 780 gets a 3349 score with a high overclock... 4316 is less than 1000 points ahead, with two cards. i dunno... you seem very low.
http://www.overclock.net/t/1360884/official-top-30-unigine-valley-benchmark-1-0
scoll down... click on dual gpu... and look down the graph at the other 290s in crossfire. you will see a lot of 780s in there but there are a few 290s... drag the graph to the right for the score/fps... it seems you are either a little low... or these other 290s are very highly overclocked.