Either of those will work, but the performance won't the greatest. But, depending on which model optiplex you have (small form factor, desktop, or mini tower) your power supply won't be up to the task of powering anything moe than the cards you looked at. They are also way overpriced! You can get them much cheaper at newegg.com. You might be able to get away with a Radeon 9600 (not the XT) without having to try and upgrade your psu.