After seeing that I’m way under powered in the GPU department (47 minutes for the render from the cycles benchmark thread) I’m considering upgrading the GPU in my Windows PC box, but not sure about the details.
Hi, your board have 2 x PCIE x16 slots which are suitable for GTX 5/6/700 series.
700 Watt is also good for one big card.
May you look for a used GTX 5/670 4 GB, I would not buy cards less than 2 GB depends on your work style.
The GTX 500 are faster than GTX 600 but are hotter and need more power.
Here is my last benchmark chart: