Over 5MH/s on 290..
and other ppl has 8MH/s for 290x and ~6,5MH/s for 280x..
They are lying...
On the 290x and 290, you can reduce power consumption by 35% and only lose 5% performance, otherwise the power bill is $$$ on those cards.
I only get ~3MH/s with this setting on my Sapphire 280Xs (3 of them). I was getting the same off sph_sgminer_x11mod. I see nothing different in terms of hashing power.
I undervolted my and with -10 C get 4.05MHs still cool and quiet.
granted there is a guy who claims to get 8mh/s with his mods but he will only sell, not give away (i have no actual way to confirm he is getting that since i dont have his modded version)
see my sig for links to my binaries and https://bitcointalksearch.org/topic/ann-sgminer-v5-optimized-x11x13neoscryptlyra2reetc-kernel-switch-miner-632503 for info about the changes to the miner