Shiva3d got some nice optimizations, that the bge could use too. Looks like the Offscreen Rendering boosts the performance of the filters, just look at the table that shows the fps with Offscreen Rendering -on/off.
Heres the link - http://www.shivaengine.com/developer/wiki/index.php?title=Offscreen_Rendering
Can the Bge get this feature too? Also check the Occlusion Culling, how do you compare it with Bge, link here - http://www.archimmersion.com/posts/tutorials/shiva3d-tutorial-occlusion-culling-and-minimap/ I think the bge Occlusion Culling should be separated from the bullet. Like having the ability the check the object that should be occluders and then bake them to save cpu, if thats possible.
Really looking forward to seeing offscreen rendering in bge. As most of the shaders don’t look worse (if not better) when rendered at less resolution. Also it will allow making render passes for specified objects only so per object bloom and related filters should be doable.
Yeah, offscreen rendering is one of the wanted features along with batching, that will bring really nice optimization speedup. 