it allowed me to do a 9000X9000 render a few minutes ago, and it allowed me to set render dimensions to 18000X18000, which I didn't try to render.  hence I dunno what the limit is.  I have seen some posts in this forum that stated various figures.  I tried "maximum render size" search for last year: no results.  some of them said poser 4 renders were limited to 4096X4096, and firefly renders were larger by some unknown amount.  no wait, I got it: set the render to 24000X24000.  see above img.

p.s. those other questions: maybe try them in the regular forum threads.  nobody is reading this thread AFAIK.