I'm driving a 2003 540i M-Sport 6 speed -- pretty much an M5 with the smaller motor. I've had a 1998 740iL, a 2000 528 and my daughter has a 325iX. They're all very different cars.
The 740 is a luxury boat that drives like a sports car. It has the same engine as your 540 so is subject to the same potential problems. That said, mine is near 200K miles and the guy I sold it to reports that it is going strong. My 540 is at 120 and going strong. If you need room for four, the 740 can't be beat. And it will still get well over 20mpg. I sold the 529 at 200K and it too was going strong.
The 530 has a bullet proof 6, with plenty of power and the previously mentioned rack and pinion steering, like my 528, it will handle better than the 540 in around town driving. The M suspension, tires, etc, make the 540 ride like the high performance sports sedan it is, but it eats low profile staggered ($$$) tires. And I must say, I'm sick of the 6 speed.
I'm pretty sure they all have the same BMW issues -- plastic radiator, front suspension that need replacing at about 100K, valve cover leaks, PCV issues, plastic water pump impeller. All are $500 plus if you have it done for you. The 540/740 have valley pan gasket issues and cam chain issues.
However -- I'm still a big fan and will buy more of them.
In your case -- the choice is really how big a car do you want?
F650GS -- sold -- what's next?
“If everything seems under control, you're just not going fast enough.”, Mario Andretti
Indulge. Repent. Repeat.