Settings for my 7850, I spent few days to get those results ;-) I'm usually mining on Windows 8, on Ubuntu I have a receive a bit lower values even with newest drivers.
SHA256 (Bitcoin) - 330-340 MHash/s
cgminer.exe -o http://coinotron.com:9322 -u user -p password -I 8 -k diablo --gpu-memclock 1200 --gpu-engine 1125 --gpu-powertune -20
Scrypt (Litecoin) - 340-350 KHash/s
cgminer.exe --scrypt -o http://featherpool.com:9999 -u user -p password -I 13 --shaders 1024 --thread-concurrency 8192 --gpu-memclock 1300 --gpu-engine 1075 --gpu-powertune -20 -w 256 -v 1 -g 1
Oh, of course there is no guarantee that you'll be able overclock your card same as mine ;-)
On default clocks (910/1200) I have similar results to yours - 260-280MHash/s.