I very much doubt you'll see that anytime soon. I talked to an X1800 engineer today at MacWorld Expo and the two cards are in different classes. The X1600 is the consumer version of the X1800, that alone makes it unlikely to be an option for iMacs, but PowerMacs will of course use them. The X1800 is a 512 MB card for PCI-Express only and is considerably larger and more power-hungry than the X1600. I can also tell you that while the demos I saw (running on a Quad G5 and a 30" Cinema Display) were impressive, there's a lot of bugs left to be worked out in the drivers between ATI and Apple. Antialiasing wasn't even working at all, for example, and I saw a number of artifacts in the rendering. Some of the shaders that will be possible will be beautiful once working, though. Now the X1600 will be able to render a lot of the same effects, but it's not going to have the horsepower to pull it off at an acceptable frame rate in many cases. Bottom line is you'll be more likely to see an upgraded X1600 in the iMacs (X1600 XT? X1600 Pro? X1650?) than an X1800.