even for oblivion or other high-end engines, hdr is a great slowdown and does not remarkably increase the picture quality (my opinion). if you want something like an "intesive lightrays" effect, try bloom.
@sinnlos sphere engine ^^ or the bloom shader that comes with the shader collection (requires renderview.dll), but i have the impression it is not that fast... any other i do not know
sylex has bloom too. Harder to handle, but it's free. Btw, you can use the Bloom in sphere also in levels that don't work with the rest of the features (=> also with levelgeometry-levels).