My wife drives a 2011 740i and I drive a 2010 535i GT. They are very similar and very different at the same time. The 740 is much plusher and more luxurious even though my 535 is very heavily optioned. The 740 drives better on the highway (like a heavy road cruiser, which it is) but also because it has the M sport package whereas the 535 does not drive as well. The 535 is taller and more prone to crosswinds, which I think is the real difference in the ride quality. But for interior room and comfort, especially in the rear seats, the 535 is better. The adjustable seats in the rear and the dual option hatch/trunk is the cat's ass. Personally I enjoy the 535 as well as the 740 with one exception. The eight speed tranny really seems to shift a lot at low speeds, which is a little irritating but is also how it gets better MPG than the 740. Overall, I think the N55 is better than the N54 in the 740 as it seems to have a flatter torque curve with more available at lower speeds.
From a driver's perspective, I thought the GT was a better ride and certainly more attractive from the driver's seat than the 535i sedan. The GT seat position is almost like an SUV but not hard to get into and out of and the longer wheelbase makes for a smoother ride than the 535i sedan. But again, the 535 GT is not the same as a 740. It's sort of a blend between a 740, a 535 sedan, an X5 and a 5 series wagon (estate/touring). The GT is a unique vehicle here in the states and I get lots of interesting looks and comments on it. Most people seem to like its looks but some think it's kind of strange looking. Here in America it has replaced the wagon, which is not available except in 3 series form, so if you want a vehicle that drives great but offers significant cargo room while not being an SUV there isn't another choice from BMW. You could argue the X6 meets those criteria but really it is a bulked up and chopped off X5 in the rear that offers terrible gas mileage, limited cargo space and difficult entry and egress. But the X6 is a great looking car with excellent road manners and a commanding view of the road.
So, the 5 GT is a great car that fills many niches and really occupies a class all its own. It is comparable to the 740 in length, to the X5 in height and seating position, the wagon in cargo capability and the 5 sedan in driving manners. I got my very heavily equipped 5 GT used (8000 miles CPO) but it does not have the sport package. I can't say it drives quite as well as the 5 sedan but bet a GT with the sports package would, as my wife's 740 with the M sports package drives as well as a 535i sedan with sport package and a little better than my GT without the sport package does.
All in all, I am very happy with the amazing versatility and gas mileage of the GT. I love the amenities, quality, power and driving position. I agree with others: the rear camera package is a requirement. I also have the lane departure warning and blind spot monitor, which in a vehicle this big is great. And I love the heads-up display, which I have never had before but my wife has had in her last three BMWs. My kids love the rear seat TVs, which do not require wireless headphones and do not play over the car audio unless I want it to... and the adjustable chassis settings (normal, sport, sport plus) really alters the driving characteristics to match the road surface I am on.
Good luck...you will enjoy this car