Can I get more than ~4,5 for r9 290 and ~4,2 for 280x x11 algo ?
Is it possible? Sure, my 280X is currently doing 4.83MH/s on X11.

EDIT: 4.9MH/s, now.
care to share your config?
try the mod version in my sig and be sure to put this in your config
"xintensity" : "64",
"worksize": "64",
"hamsi-expand-big" : "7",
"hamsi-short" : true,
"blake-compact" : true,
"keccak-unroll" : "8",
"luffa-parallel" : true,
"gpu-threads" : "2",
I worked off of yours, I'm pretty sure my X11 is in the ballpark of 35.20% faster. X13 around 38.51%, and X15 about 42.87%.
with mine you should get 5.2mh/s on x11 with 290 (stock clocks) and 6.2mh/s on 290x (oc to 1040/1375)
What about 280X?
EDIT: I cloned the develop branch of your repo - is this a joke? 4.55MH/s on X11 on my 290X, tops. It's at 1000/1500.
EDIT2: Though I am liking the xI 64 - getting 6.14MH/s almost on my 290X, 1000/1500.
use the master branch... although it shouldnt be too different
i get 5.8 to 5.9mh/s on my 290x with 1040/1375 and I 16
and 6.18 to 6.2mh/s with xI 64
edit: my mods arent on the develop branch anymore as i started over with the 5.0.0 update
All right, I'll give it a shot later. Getting 6.15 with mine on 290X now, at 1000/1500, so still not bad.