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 (5.2mh/s on 290, 6.2mh/s on 290x)
"xintensity" : "64",
"worksize": "64",
"hamsi-expand-big" : "7",
"hamsi-short" : true,
"blake-compact" : true,
"keccak-unroll" : "8",
"luffa-parallel" : true,
"gpu-threads" : "2",