go to my website below and read under
Tips : Before you buy
covers the 735, 740 and 750.
The 740 is the more modern engine, but the old M30 straight six is the iron horse in the stable and used in many BMW models.
Maintenance is cheaper (also easier DIY), and much more used parts are available.
I would tend to the 735.
Boot of the 7 series is larger, as you can imagine.
Basically - as you drive an 535- there will be no big surprise for you, many parts are interchangeable with the E34.
The 7 is bigger and more comfortable, more legroom in the rear.
Stay away from cars with EDC shocks, very expensive to replace, costs same as a complete new car.
Or you replace them against standard shocks.
In case you buy an iL, legroom is again larger in the rear, but all iL have LAD = self levelling for the rear, these shocks cost about 500 $ a piece.
But mine last now almost 20 years, but less than 100k miles so far.