What's in the rest of your system? 17A isn't too bad under certain conditions. And do you have a 12V1 and 12V2 rails? If so you might have more amps on 12V.
Something like a 6600GT, 7600GS or HD2600 Pro may work.
My HTPC only has 10A on 12V and it runs a dual core CPU and a X1650 Pro.