When mining Vertcoins I have found it is very important to use the right Catalyst drivers, so please post OS and driver version with your settings.
I have been struggling with my hashrates, but just as an example I have 5x R9 290 (in two different systems) under Windows 7 ultimate 64 bit.
With stock speeds, intensity 17, tc 24550, w 256
Catalyst 14.1 gives around 250 khash/s
Catalyst 13.12 gives ~300 khash/s
Catalyst 13.11 beta 9.5 gives ~400 khash/s
So, if you feel you are stuck and have tried everything - don't forget to try different drivers as well.