I have apes on my bike. They are 18" from
www.LAChoppers.com . I love the bars. I had the same back pain you refer to. I could have gone with chubby non-ape bars, but I have always liked the look of apes. I am 6'1" and my grips are right at my shoulder. They are my favorite addition to my bike. But, apes can be an expense. You will need new cables and to extend your wiring. It seems like an easy enough job to do it yourself, but I was unsure about it, at the time. I paid an Independent shop to put them on. For everything, it cost me $800. If I was to do it all over again, I would do it myself, and save nearly half the cost. Since the time I had them put on, I have become pretty sure of what my abilities are, and I could do it myself, I am sure. But, it is done, and I am very happy. If you get a chance, hang out at a dealer or bike night, and find someone with apes. Ask them to sit on their bike, most will not mind (I don't). Just make sure it is a touring model, since the ST and Dyna's sit you differently. But, in answer to your post, depending on your height, I would go as high as what is legal. Otherwise, I will bet, you will have wished you went taller from the beginning.