For 2013, the BMW 5 Series GT lineup gains stop-start ignition and the new Eco Pro system in an effort to increase fuel economy.

Small, medium, large and extra large; these sizes tend to fit a variety of needs. Be it clothing, soft drinks and yes, even cars, most people will find what they need. But what about a half size, perhaps something that slots between large and extra large?

That's the issue we have with the 2013 BMW 5 Series Gran Turismo. It's based on the 7 Series sedan, and features a hatchback body design for more cargo versatility. We're left pondering if this middle ground really needs representation, though, especially when the 5 Series GT costs quite a bit more than BMW's own X5 and X3 crossover SUV models.

The Gran Turismo's dual-mode hatchback is an intriguing model of innovation. From outward appearances, one would assume that access to the cargo hold is just like that of a hatchback, and you'd be correct. The hatch is also hinged at the base of the rear window, however, allowing the tail to be popped open like a conventional trunk. BMW contends that this allows the passenger compartment to be isolated from the elements when loading standard cargo, with the ability to haul larger items when the need arises.

Classified as a large luxury sedan, the five-seat 2013 BMW 5 Series Gran Turismo features a segmented rear window and deck lid that can be opened either like a hatchback or a conventional trunk. Trim levels correspond to engine choices and both 535i and 550i models come standard with rear-wheel drive, with all-wheel drive (xDrive) available as an option.

Standard 535i features include 18-inch alloy wheels, adaptive xenon headlights with washers, foglamps, auto-dimming and heated exterior mirrors, a panoramic sunroof, front and rear parking sensors, automatic wipers, leather upholstery, a power tilt-and-telescoping steering wheel, dual-zone automatic climate control, 10-way power front seats with driver memory settings, and sliding, reclining and split-folding rear seats. Also standard are Bluetooth, BMW's iDrive electronics interface and a 12-speaker sound system with HD radio, a CD player and an iPod/USB interface. Besides the upgrade to the V8 engine, the 550i adds 14-way "multicontour" front seats, a rearview camera and navigation with voice recognition, real-time traffic and online information services.

Most Gran Turismo options are grouped into packages. The Sport package adds 19-inch wheels (or 20-inch wheels for the 550i only) with performance tires, gloss-black exterior trim, multicontour front seats (otherwise lacking in the 535i), a sport steering wheel and an increased top speed limiter. To that list the M Sport package adds M-specific wheels and steering wheel, an anthracite headliner and an aerodynamics kit.