I know you didn't want i said, but you can get an exceptionally better pc if you build it yourself
I think Asus does build the best Pre built PCs.
If you have an old pc in your house, Watch a couple of youtube videos and see if You can disassemble and reassemble it. It isn't as hard as you think.
If you need help, @Doc Lives in Australia and I'm sure he'd be happy to help you out when You needed it.
The main problem with Pre built PCs is that they lack the Graphics. You'll end up having to pay for a new Card by the end of the year.
The first one has 2.9GHz 4GB of ram and 512MB GFX So you can pretty much count that out compared to the others
Why did you not pick this one as 1 of the 4?
Asus Essentio CM6730 Desktop Tower - Desktops - Microsoft World | Harvey Norman Australia