Top Left is the reference/start image
HDR moon-bluegrey.hdr (Horo)
Render time 28:34
Top Right I've dropped the Quaility to 0, changed the HDR to St peters which is naturally bandy anyway and used the reflective chequed floor to disguise the quality issues as in the previous example.(also had to lower the intensity to 30 to compensate for different brightnessess in the hdr).
Render time 1:20
Bottom Right as top right except I've switched on the HDR to be rendered as a background option. Note the highlights on the reflective and transmissive spheres.
Render time 1:33
Bottom Left as a final emblelleshment I've lowered all the diffuse channels of the materials by 50% and put in a none diminishing off white light source with an intensity of 10 above and to the right of the perspecitive camera. The purpose of this is to stimulate speculative response in the glass and metal spheres which I believe makes them look more realistic.
Render time 1:35
Conclusions... well to be fair this is highly subjective but I'd say that with a little ingenuity it is possible to reduce render times for IBL renders by a factor of 20 without any detriment to the quality of the final image. Of course if the purpose was to stick with the origional format then this would not be possible. Just something to think about.