After experimenting with a long running average at maxed out FPS and a variety of map sizes, 128 seems to actually be a good size to use if only drawing bits of world with stuff in it. 64 actually did even better in some situations, but significantly worse in others (lots of land, zoomed out).
FIND_PATH(GMP_INCLUDE_DIR gmp.h)
FIND_LIBRARY(GMP_LIBRARY NAMES GMP gmp)
IF (GMP_INCLUDE_DIR AND GMP_LIBRARY)
SET(GMP_FOUND TRUE)
ENDIF (GMP_INCLUDE_DIR AND GMP_LIBRARY)
IF (GMP_FOUND)
IF (NOT GMP_FIND_QUIETLY)
MESSAGE(STATUS "Found GMP: ${GMP_LIBRARY}")
ENDIF (NOT GMP_FIND_QUIETLY)
ELSE (GMP_FOUND)
IF (GMP_FIND_REQUIRED)
MESSAGE(FATAL_ERROR "Could not find GMP")
ENDIF (GMP_FIND_REQUIRED)
ENDIF (GMP_FOUND)