The current limit here is up to 1280 x 1280. In other words, neither the width nor the height can exceed 1280 pixels. I don't know if FA automatically resamples a new submission down to the allowed size, or if the submission is simply rejected at the time up uploading. I never tried to test it.

Is it something that can be split into sections? That would require splitting into six sections, like pages in a book.

It rescales images that are too large (sometimes badly). I think there's a trick to get around that by editing the submission and re-uploading the file, but I've never tried that myself.

Another idea is to submit a small portion of the image and link to the full version (hosted elsewhere) in the description.

Depending on how it's made, you could also submit it as a simple flash movie and divide the screens

you can chop it up in segments.

I always work at a larger size but then scale down the final image to meet the required 1280x1280 resolution for submission.

I know Kah is doing it : http://www.furaffinity.net/view/5146060/

So, I suppose as long as this workaround doesn't get abused, you might be able to use it.