well, i have the CT for one year now - for the wife - and had a 730d from March 2015 till last month. Before that had a lexus GS250 and an IS250 I am waiting the 740d xdrive msport early September, immediately when 67plate kicks in. All vehicles bought brand new
the GS building quality was superior. Was also smoother cruiser at speeds up to 80mph aBMWnd much quieter ( tyre noise in the bimmer was much louder)
BMW was obviously much much faster ( and that is why I do not really believe that IS250 0-60 is in the low 7's as the 730d is around 6.5 and felt like a rocket in comparison) and was holding the road better in fast turns, higher speeds etc ( had the adaptive sport suspension)
BMW reliability not bad but a few hickups. To start with, some annoying noises very early when driving on uneven ground. GS was completely silent . That been said, CT does squeak as well, so a bit disappointed there
BMW spec much better. the infotainement though once a month would go suddenly off for about a minute. No satnav, nothing. Then it would start over again on its one. HUD stopped on a couple of occasions ( bizzarly after I put diesel on a specific gas station , after stop visiting this, never had a problem with HUD. weird stuff)
Brand image, much to my surprise BMW was is way ahead. Nobody could care less about the GS, had people at work asking me about the 7 series
real life MPG BMW was about 39, mostly motorway. The GS was about 29
hope that helps
edit: and the BMW speedometer is much more accurate than Lexus. Real 30mph is 31 in BMW and 33-34 in Lexus