For you uses think hard about a raid 0 array instead of a single disk. Video edit stresses disk.
In the first build make sure you have a good 2TB 7200 rpm drive not a 'green' or 5400 rpm drive.
In the second build - no way i'd use liquid cooling for anything. Eventually the liquid is coming out. Buts that's just me.
Suggest you check your favorite video software and see what video cards can be used to accelerate processing. You might discover that strong video is more improtant than you think. A highly parallel video card might work better than the same work done on the CPU. In 'folding at home' the GPU client kills the CPU client.
I googed the costco system "Online price $949.99 Less -$250.00 YOUR COST $699.99." so the price is nice. The online reviews were bad. Teh MB was h67 based (good) and you can replace a cheap PSU with a good one for $70 or less if ou need to. That said, i'd read reviews very carefully and plan on doing my own service if it fails. http://www.costco.com/Browse/Product.aspx?prodid=11673224