set the “percentage scale for render resolution” (render/dimension) over 100%… but I never tried it
or try this:
can render to n times your original rendersize.
if your render dimensions are 1920x1080 and check “use render dimension” and set multiplier to 8,
this script render 64 image (one for each region)
and, if you have imagemagik installed, join all in one image 15360x8640
I tried it and it works in 2.58 and 2.57.
the script is more safe, with big render, with a lot of objects, textures, not enough memory…, blender crash when save the big image; no crash saving many “normal” or small images
and sorry for my english…