+1 also I think the intensity can be increased, after the N-factor change I didn't modify my config and got no HW
290 is almost the same as 290X so I think it can take higher intensity so you need to balance worksize and thread concurrency
my card has tc 30592 by default so you should look into adjusting that to get higher hashrate because in my opinion with tc 20480 , they are underworked...
Yes if you have plenty of ram you could change to --Thread-Concurrency 32765 -I 20
Not sure if that would change WU much though; one could try both variations I suppose.