Making big images

Recording at 1920 x 1080 (HD) works fine. On the hot rod, I get almost 2 FPS uncompressed and around 1 FPS using XVID. That seems pretty damn slow, but it's about 3000 times faster than Electric Sheep. The question is whether 1080 is good enough for generating poster-sized images, e.g. 11 x 17 at 300 DPI. HD 1080 is only 6.4 x 3.6 at 300 DPI. I tried 5100 x 3300 and it didn't seem to work even on the hot rod. There was memory to spare, so I'm guessing that the exponential increase in compute time would mean render times on the order of an hour per frame, like Electric Sheep's. It would be interesting to see whether it eventually coughs up some frames.