Hey - nice picture!
I seem to remember that this is the one that pushed you into buying the 9900.
The biggest picture that I almost printed in Lightroom 3 was a pano of 80 stitched images. Flattened to one layer, and imported into Lightroom, it was 18,000 by 8,000 pixels (the file size of the flattened version is about 1.5 Gb). When I tried to print it with Lightroom upresing to 480 dpi, Lightroom chugged and thought for a while, using lots of memory and CPU cycles, but never fired up the print driver. When I tried it with Lightroom upresing to 360 dpi, it printed a completely blank canvas.
At that point, I gave up, sharpened in Photoshop, and printed it. Although I usually like to upres to 360 ppi or so, I found that Fractals (now Resize) didn't improve the microdetail, so I just printed at 180 dpi, and to my eye, it was OK (this was on canvas, which I can't seem to get the same kind of detail on as with a good paper).
My unsuccessful Photoshop attempt was a pano which was 32760 pixels in the long dimension. This was before I owned the 9900, so I didn't do the print myself. The person who did the print couldn't get it to work until I downsampled it to a bit under 30,000 pixels in the long dimension. Even with downsampling, the print was 320 dpi, and looked great (this was on paper, rather than on canvas). This was with CS4, and "Farmer" kindly advised me earlier in this thread that CS5 x64 should be able to handle a file with this pixel dimension.