Mike, I bought the 17-70 Sigma on Terrys (CometGuy) recommendation some time ago, I bought it from my local Camera shop for $470 after finding a price in Oz on the net of $460 delivered free (which I suspect was a mistake). I simply asked my local dealer if he could come up with a close price, not necessarily cheaper and he obliged. I'm very happy with my lens, compared to the standard lens it is very good. I can't say I've noticed any barrel distortion but if apparent, it's easily removed with photoshop. BTW
centre.net.au have it for $477.95 at the moment. Shipping to Gosford overnight is $13.