Buying the 400r is pointless. I would be curious to know the weight and dimensions of the 650r motor to the 400r. I can't understand the weight similarities between the bike.
If the op was happy with the ninja 500 she should consider:
http://www.topspeed.com/motorcycles/motorcycle-reviews/suzuki/2010-suzuki-gs500f-ar45565.html
[TABLE="class: specs2"]
[TR]
[TD="class: white_right"]year:
[/TD]
[TD="class: white_left"]2010
[/TD]
[/TR]
[TR]
[TD="class: blue_right"] Torque @ RPM:
[/TD]
[TD="class: blue_left"]30.4 lb-ft @ 7,500 rpm
[/TD]
[/TR]
[TR]
[TD="class: white_right"] Horse Power @ RPM:
[/TD]
[TD="class: white_left"]51.3 hp @ 9,500 rpm
[/TD]
[/TR]
[TR]
[TD="class: blue_right"] Engine:
[/TD]
[TD="class: blue_left"]twin-cylinder, 4-stroke, air-cooled DOHC
[/TD]
[/TR]
[TR]
[TD="class: white_right"] Transmission:
[/TD]
[TD="class: white_left"]6-speed constant mesh
[/TD]
[/TR]
[TR]
[TD="class: orange_right"]Curb Weight:
[/TD]
[TD="class: orange_left"]199 kg (439 lbs)
[/TD]
[/TR]
[TR]
[TD="class: blue_right"]Energy:
[/TD]
[TD="class: blue_left"]BSR34, twin carburetors
[/TD]
[/TR]
[TR]
[TD="class: white_right"] Displacement:
[/TD]
[TD="class: white_left"]487cc Cc
[/TD]
[/TR]
[/TABLE]
It's a similar bike, the weight and displacement are the same. The fuel economy is better than the ninja 500: 59 mpg.