I've done a 4000x3000-ish render, but like you I had to do it in strips and join it back together at the end(but then I've been doing that for 4 years so it doesn't worry me having to do it that way). The biggest single render images I've done were about 3000x2700 but they were really simple images (1 terrain, 1 ecosystem sort of things). I tried a 6000x2700 of the same sort of image, but that suffered the Vue version of explosive decompression every time.

Dreams are just nightmares on prozac...
Digital WasteLanD