Yeah, if you can afford the XT, get it... if you can't save money and get the GT. Mine OC's very high, up towards the 650 core range... not sure about the mem.
xt is the best. The XT has more pixel shaders. The GT and Pro have the same pixel shaders, but the GT just runs at lower clock speeds. I have a gt and it works great in most games at 1280x1024, and it overclocks fairly well.
Stay far away from the GT and pro if at all possible. Some of them have problems running stock out of the box, some of them wont overclock at all, and the ones that do usually don't go that high, I would know since im on my second x1950pro.
The x1950xt is better than the other two, in every way except for heat output and power usage.
Get the best one you can afford, which is the XT in this case. If you find the stock cooler too noisy, there are a plethora of aftermarket ones out there.
The pro if you wanna crossfire, the xt if you don't. Also, get one of 512mb editions of either. Games will thank you, especially if you are running widescreen resolutions.