Do you want a 30-incher with 2560*1600 resolution or rather a 26-28-incher with 1920*1200?
For 25*16, you really need a top SLI/CF/4870X2 setup to play at smooth FPS and in eye candy modes. For 19*12, a weaker card will do (I guess you'll be upgrading your X800 to a current gen card). 30" also means very small pixel pitch (0.251 mm), something to consider.
I personally prefer 26-28" 1920*1200. IMO, the best monitor in this range is currently LG W2600HP, based on H-IPS panel which means great viewing angles and colors, good contrast and in this case, a moderate price (but still about 50% higher than a 26" TN). Very good reactivity plus no input lag make it a suitable panel for gamers. The ViewSonic VX2835wm and VX2640w are also decent alternatives but both are based on TN panels which mainly means poor vertical viewing angle. However, if you're sensitive to input lag, forget the 28" model, as well as the Dell 2709W, which, if input lag was eliminated, would be one of the best gaming monitors in this size range.