1m /335is radiator fan is a plug and play part. This poster claimed ~15F idle temp reduction and mentions anecdotes it helps for track use also.
http://www.e90post.com/forums/showthread.php?t=591900
I wonder if that fan plus lower temp thermostat (maybe from m3?)or the thermostat bypass would solve e89 oil temp issues for far lower cost without having to go with aftermarket $$$ oil cooler kit