I'm on 13.9 as well. -i 13 gives me about 330kh/s. Starting up with -i 13 may help and then switching to 17. I'd go higher, but this is also my main desktop and 17+ starts to kill performance. It seems like most of the 280x configs use -i 13, 8192 tc, and -g 2, but I think those have all given me worse performance on my 7950s.. I'll give I 13 a try in a little bit though!

Thanks!