I just updated to 240e (latest). You need ICOM cable and a good charger. Engine & dct updates are pretty quick (total an hour) so you might be able to get away with just making sure you battery is topped up b4 you start.
Don't know if I've noticed any performance improvement, but I really haven't had a chance to do any good pulls/spirited driving yet. Haven't noticed any lagg in 2nd gear in auto mode, will have to try manual. There really shouldn't be.
I think people with really old software (08/09)have been saying they get some noticeable improvements. One guy even dyno'd a +20hp gain, which is pretty incredible
E92 ///M3 in Dakar Yellow, M-DCT, iDrive, 220M OEM rims, Active Autowerke Green filter, Turner Motorsport test pipes, BPM stage 2 tune.