I would go with option 2. Subject to finding out exactly which model of Silverstone PSU is being offered OR getting a good 650W PSU in it's place. Hopefully this change will give you some more money to alter other parts in the build. You could make the same change to the first build as well.
I suppose it's possible that the extra $100 could ensure that you get a fast harddrive and get you CPU cooler. The MSI P55-GD65 is a good board, but the Asus P7P55D-E Pro has the advantage of SATA 6Gbps. The MSI board is much better than the Gigabyte board in the first build.
If you are going to overclock then you probably would want to get the Hyper 212 Plus. Otherwise it's not very important.
1) A corsair 750HX PSU is about as good as it gets. But, do you really need modular, or that much power? A 650 watt unit will power the strongest single graphics card you can buy today. Modular is OK, but with a properly sized psu, you will be using most of the leads anyway. It is not hard to tuck the unused leads away.
2) The gigabyte motherboard is good, and it includes usb 3.0 and some 6gb sata ports. What more features do you need? Your cpu will run the same speed, regardless of the motherboard.
3) You get a decent oem cpu cooler. It is best to install one during the initial build while the motherboard is still out of the case. Your PC will run cooler and quieter and if you OC, you
can go higher and easier.
4) The XFX 5850 is a bit better. It is the factory overclocked version and XFX has a double lifetime warranty. (Is this still true in Australia?) I do not see the performance difference as significant.
5) Check on which version of WD hard drive is offered. The green is slower to be more energy efficient, the black is the best performer, and the blue is in between. I would opt for the black which is slightly more expensive. Perhaps even the 1tb model which is a bit faster.
6) If you have some extra budget, consider a intel X25-V 40gb SSD(or two) for your OS and a few games. Newegg had them on sale here for $98. Anandtech had a glowing article on this. http://www.anandtech.com/show/3618/intel-x25v-in-raid0-...
See if each shop will adjust it's bid to your specs so you can compare them directly.