I will throw my .02 in... being I am 5'7" short myself.
I'm guessing you are leaning forward and slouched a bit? lower back tends to get sore after extended rides?
A few tidbits of info to consider:
Pullback affects wrist angle....tends to force your elbows in toward your body.. almost to an unnatural position. BE CAREFUL on too much pullback on your selection.
Rise of bars will affect how you sit when static, in relation to positioning within the bar clamp... too far forward you lean forward with wrist angle being thrown outward....and too close you hands are lower and wrist angle is affected inward.
i went with 12" Yaffe Monkeys after sitting on many bikes with different bars. Each bike I sat on were setup for the particular rider, but you can get a FEEL for height and wrist angle pretty close. 12" YMB's have a 6-7" pullback ( can't remember exact)
Reason? Hands were just below shoulder height with elbows slightly bent sitting naturally with no lean forward or back. This was a very comfortable wrist angle for me as well. Sitting on someone else's bike gets you close... not perfect.
After initial install and setting up for LOOKS ( visual pleasing to the eye in relation to bodylines and orientation ) they were too far forward and I leaned forward. Back was screaming after 30 minutes! I was not happy with position.
So I loosened the clamp, rotated the bars toward me about 3" from the top of the fairing and snugged em up... now I was sitting upright, elbows slightly bent and comfy.... GREAT position! Tightened up the clamps and rotated the controls slightly to get a better position of hand controls, clutch and brake levers.
After this second go... I never touched them again.... PERFECT position on all aspects.
pic of me riding for reference:
Now keep this in mind... factory bars are approx 8"... if you go up 2" from EXACT position, the bars are about 1" closer to you... go up 4" ( 12" bars ) they are about 2" closer to you over factory. Take into consideration you can STILL ROTATE THE BARS CLOSER if you need them (which I did ) to get MY POSITION comfy.
Going UP in height of bar size isn't ALL about the look, comfort is a key factor as well.