What about the upgradability of these builds? The mobo for the $500 one supports USB 3.0 and SATA 6.0Gb/s which is nice..
And what exactly does 2 GFX cards (as opposed to 1) do? I've seen builds that have 2 graphics cards..
Also the $500 build doesn't have a case..
the 500-600, you are able to upgrade to bulldozer when it is released, you will be able to upgrade to more memory, and faster memory, and you will be able to put in a second video card if you wish. There is also room for an after-market CPU cooler, more hard drives for storage, or later on an SSD.
It is the same for the others, only you will be able to upgrade to an i7, and the revised versions of the Sandy Bridge CPU's when they come out, which will probably be next year. The i5 will hold you over for a hell of a long time though.
Multiple graphics cards can work in one of 3 ways:
Firstly, where they work separately, which is purely for extra displays. Most users won't need this, because it is only if you are going to have a lot of displays. Bare in mind most will support at least 4 monitors.
Second, where they work together to act as a single card. This will lead to more powerful graphical processing. It doesn't work out 100% gain over a single card, because a part of the performance is lost, but it isn't far off 100% for the latest series of graphics cards. You can't use any old graphics cards though, they must be the same chip. They can be from different manufacturers, have different amounts of memory or be clocked differently, but they must have the same chip. You can tell whether or not they will work by the first 2 numbers:
for example, a 6950 and a 6970 will Crossfire together
2 GTX 560's will go in Crossfire together, as will a GTX 560 and a GTX 560Ti
Thirdly, is if you have a dedicated Physx card. Physx is a technology which Nvidia own and is utilised by some games to add more realistic effects, such as fluid water and clothes, more realistic explosions and debris and more realistic smoke, sparks and other effects. As this is Nvidia only, you would get a dedicated Physx card if your primary card is AMD, or to take load off the primary card. As it is only processing Physx, you would be able to have, for instance, a GTX 570 + GTS450. The 450, even though not the best gaming card, would be there just for Physx. the 570 would take all of the shading, textures, tessellation etc processing, and the 450 wouldn't work with the 570, but it would do some of the physics processing if the game supported Physx
For the case, it was the CM 690II for both the 500-600 and the 1000
