Not sure I like the idea of lowering the oil temp that much. I would imagine BMW had it in that range for a reason, and I seriously doubt oil temp affects emissions. Coolant temp yes because it directly affects proper combustion, oil temp I doubt it.
Also, there seems like there's quite a bit of fab work involved for the replacement. The Dinan kit seems to mount to all stock locations, but I can't tell if requires the removal of the front crash bar to install it or not, although that doesn't seem to be the case. Obviously this kit requires the bar to be removed because it mounts behind it, but I can't tell from the install if that was required to remove the stock oil cooler or not.
Another question I have is why everyone is caught up on the Setrab oil coolers. It's not they are the only company to make high quality high pressure oil coolers. Derale has made them for years and their cores certainly cost quite a bit less. I guess I just don't see the appeal of paying that much extra for an oil cooler just for a name.
Based on the pics of the stock oil t-stat, a properly sized replacement spring could do the trick if you just want to lower the temps without the hole filter housing replacement. Sounds like a fun project to me.