PCI-E is backwards compatible and is specifically for the motherboard. If your video card is PCI-E 3.0 it will work in a PCI-E 2.0 slot and 1.0 slot.
There are rare issues with 2.1 cards in 1.x slots.
Make sure you read this thread, I have answered this particular question for another member:http://www.tomshardware.com/forum/360499-33-dual
In regards to CPU, anything higher than a i5 2500k or i7 2600k will do good.