So far I've found the sat nav on my 2013 car better than the BMW version I had updated. The Lexus takes full postcodes whereas the BMW only did once I updated it and even then it would struggle finding some destinations. I actually prefer the Lexus sat nav - the traffic updates and mapping display I much prefer. I had the Harman Kardon setup in my BMW and I think the Mark Levinson has the edge too although occasionally it sounds a bit tinny when the source is of low quality. Plus I've not got DAB which was an optional extra with the BMW.
Styling wise, even though I had a 2010 BMW, I think the styling was a little more current that the ISF - inside for certain. The controls, switchgear etc are also a notch above in the BMW I felt. I do feel like i'm sat in a bit of an outdated car with the ISF - much like I was when I had a 2008 Honda S2000 that first hit the showrooms in 19999 and didn't really change. But I actually love the feel of the ISF in the cabin as it seems so well built and quality.
Performance wise, the M3 had lots of settings that you could tweak from suspension to response of the engine to gear changing frequency - I could tailor the sport button (or M button) with lots of settings. As far as I can tell, I don't have any way of tailoring the sport button on the Lexus? In Drive mode in the BMW with the 'sport' setting it would pickup so much better when you planted your foot down - noticeably more than the ISF at motorway speeds although similar when lower down. Although the M3 had a great sound - the Lexus above the 4k rev range makes a great noise - better than the M3 and that was some sound - but both are very aggressive. Handling wise (not that I've been on a track) it all seems very similar and so does the comfort. I know my version has a diffferent suspension setup but it's no different to driving the M3 on its middle setting and probably more forgiving than the M3 in true M mode.
Overall, I'd take either car to be honest. If the M3 came with a lifetime warranty or a Lexus priced warranty then possibly that would get my vote for more customisation with your drive. But, because it doesn't and because a one year warranty without an excess costs £1500 for a 2010 car then the Lexus is an absolute no brainer - particularly with the current warranty of 900 for 2 years!
But yeah, both great cars and have no regrets moving to the ISF....other than the second rate MP3 setup and not being able to customise my drive settings so much.