I was wondering if this processor IntelŽ Core™2 Duo Processor E8500 (6MB L2 Cache, 3.16GHz,1333 FSB rather than the Q6600 would cause a significant performance change.
It depends on what apps you will be running. For media encoding and editing, you'll be better off with four cores but games will see better performance from higher clock speeds and not extra cores. The E8500 is a great CPU.
Will SLI really boost performance that greatly compared to a single GPU? I ask because there is a lower end model without SLI capabilities and its a like a hundred dollars cheaper. It has the same quad core CPU available or a IntelŽ Core™2 Duo Processor E6850 (4MB L2 Cache,3.0GHz,1333 FSB) which is slower than the previous core2duo that was mentioned before.
The thing about SLI and CrossfireX is that they are very unpredicatable. Performance gain can vary greatly from game to game. But you're never likely to see more than a 50% gain from adding another 8800GT. The general saying is that one powerful card is always better than two lower powered ones, plus becuase your buying it from Dell, they'll probably have put in some shitty 650i mobo which only has 16 PCI-E lanes. (8x + 8x SLI mode). It's because of small things like that and for exemple, the PSU (which is one of the most important components) will be a no name poor quality unit to keep costs down. The RAM will also be generic and have high latencies, I could go on and that is why I would like to echoe the others who have responded to this thread. You are better off building your own, you can get much higher quality parts for less and you won't have the embaressment of having bought from Dell.
If you think it's way above your abilities, have a look at this guide: http://www.buildyourown.org.uk/
Ask away if you want to know something else.
Here's a quick list from Newegg, for $100 less, you can get a Phenom 9850 (outperforms the Q6600 in most benchmarks) and a CrossfireX motherboard which allows you to join up to 4 HD 3000/HD 4000 series GPUs. The PSU I included is also a lot higher quality than the one Dell would supply and I just got the Gigabyte 3D Aurora and it's an awesome case. All aluminium, full tower with loads of really well thought out features, I have the black one though.
And for the graphics card, I included the 8800GTS 512MB but the ATI HD 4800 series will be out this month and they are looking good and yields are reportedly excellent. All the information I could gather on them is in the two pages of this thread: http://pcdiscussions.myfastforum.org/about12.html
Oh, and before anyone says "Why did you pick 1066 RAM? It's exactly the same performance as 800" AMD Phenoms have a built-in memory controller which allows them to send and retrieve data from the RAM without going through the FSB and north bridge like on an Intel platform (this restricts bandwidth and increases latencies). So the Phenom will benefit from 1066 RAM especially because of it's 2000MT/s memory controller speed.