For the moment ONLY nVidia GeForce cards are advised. CS6 does not support AMD cards and AMD is still considered the 'New kid on the block' as far as CC goes. AMD is still in its infancy, the drivers and Adobe support is still too new to effectively compete with nVidia's CUDA acceleration, which has been proven in the past years and have stable drivers from nVidia and stable support from Adobe. nVidia CUDA support is a mature technology with a proven track record. Add to that the recent price increases of AMD cards and they have effectively outpriced themselves in the competition with nVidia. Initial benchmark results with AMD cards show they are about two times slower than equally priced nVidia cards.
You'll want to add at least 16GB more RAM as well.
You have not mentioned what kind of media you intent to edit.
You really need a second storage device, hard drive at a minimum or SSD
what version of Premiere?