Sounds like you've chosen some good components. However, you should sit down and actually write down what your needs are now and what you anticipate for the future so you buy right now. By the time you are done getting the hard drives (you should have more than one), the DDR3 memory (you have no choice), case, CPU cooler, OS, monitor (?), DVD burner (Blu-ray $++++) and the other odds and ends you will probably easily bust $1000 though. I just built a new box to run the lowly Pinnicle Studio 11 Ultimate (Avid's little brother) with the hope of eventually running apps like yours. Here's my setup: C2 Quad Q9300 (FSB excellent for editing speed), DX48BT2, 4G DDR3, ATI 3870HD 512MB DDR4, Cool Master Cosmos 1000 case, 750W power, 5 HDDs (2 Raptors [partitioned RAID 0 for OS and programs], 3 500GB WDs (partitioned perfectly just for editing/rendering/storage), Vista Ult. 64, and assorted DVD drives, coolers, etc. and spent about $2200 between TD and Newegg. Now I have an almost filled up full tower. I don't know how you plan to expand in the future but you can only add one more PCI (black slot) for sound or whatever. If you are doing a lot of editing and saving make sure you have space in your box for more HDDs or you can use the eSATA for external storage - no problem there.
New additions of CS3 and Avid will run nicely on what you have chosen. My transition rendering is less than 2 seconds and you should come close to that. Keep in mind that if you are using this computer for all kinds of other stuff such as gaming or other high demand apps you may very well crimp your editing style and speed. Plus your 2 vid cards won't push you but so high. You might consider getting a 512MB or more now and Crossfire another one later on for blazing performance if you like.Â
One last time I will stress that you Write Down what you need now and what you want for the future. That's the best way to decide what you can afford and get now so you will be prepared for the upgrades you'll want soon enough. GOOD LUCK!
