Currently, there is a Geforce4 MX440 in my AGP slot. I'm looking to make a slight upgrade. But I want to know which is better, the X800GTO (here) or the X1600 Pro (here)? My next question is: I have a Dell Optiplex GX270. According to Dell it came with a 250 watt power supply. Will either of those two cards be able to run with that power supply (my guess is no). If my guess is correct would replacing the Geforce4 MX440 with a X1300 (here) be an upgrade? If so, would the X1300 be able to run on the 250 watt power supply?
that power supply is going to be a problem, you really need to upgrade that, out of what you listed i would go the 800GTO route but not before upgrading the PSU or else you could run into power problems.
What else is in your Dell drawing power? You may have problems finding a non-Dell power supply to fit in your case, but it's possible the 250 is enough. You should be able to find the power spec's for the cards on ATI and nVidia websites to help you compare against the 4400. I'm not sure about the X1300, but the X1600 requires an available 4-pin power plug. As long as you can return a card, just try it for a couple days.