To me, a position with the feet even slightly forward has always given me problems with my back. Basically in that position, any bump goes straight to the back bone, whereas with feet placed straight down or further back and having the legs properly bent, it is the legs that take the shocks resulting in no back pain.
I am 187 cm, which is something like 6.13 I gather, so fairly tall, but have mostly been riding either sports bikes or "Euro" roadsters. So, pretty much always with well bent knees and feet more to the back. I hate the position on cruisers, but that is just me. With age, I have found that some have me bending the knees a bit too much, giving me serious pain in the knees after a while. Being prone to regular back problems (I have a vertebrate to many in my back bone, and a pretty serious scoliosis) getting on my motorcycles have always helped ease the pain in my back. There have been days I simply couldn't get in to my car to go to work, but getting on the bike was fine.
My CB1100 certainly has not given me any back pain. Like Ferret says, you need to keep a proper posture on the bike and not let the back "slouch". Doing that, and then letting the wind hold you up is perfect. If anything, I would actually prefer slightly lower bars rather than higher, and no windscreen. But then, I also avoid riding straight highways to the extent I can, and stick to twisty roads whenever I can. The twistier the better!
