There is no set startup screen limit, but you may be running out of RAM.
Your limiting factors are available RAM and heap size. You need to have
enough RAM to load your System file, Finder, any INITs or CDEVs, and any
RAM cache that might be set in your control panel.
Another possibility could be your system heap needing resizing to
accommodate such a large startup screen. Apple does not support changing
the heap size, but there are several third-party utilities that do this.
For more information, search on "CE Software".