bikes with short top tubes

I have a similar problem with stretching out on bikes. Essentially, I've got long legs and a short body. I've found smaller frames more comfortable, but you have to use a longer seatpost to compensate.

Also, modern bikes come with inordinately long stems compared to times gone past. An old run-of-the-mill racer would have a 70mm stem and you could get shorter ones at 40mm. 100mm was a really long one. I know it's splashing out more money, but you could try a much shorter stem.

To help with the back pain, do try stretching out your hamstrings and glutes after riding. The combination of big strong thighs and glutes with weak hamstrings (naturally caused by cycling) pull the spine into a horrible shape. Stretching will significantly reduce the effects.

After loads of tweeking I've found this set up to be the most comfortable on any rides over 2 hours in length. Modern bikes tend to be too stretched out for my hobbit physique Highly recommend the more upright position despite the piss taking involved...

Does look a strange set up....

Old school tt bikes generally have short top tubes. For comfort (lack of flexibility) a general rule of thumb is to get the bars the same height as the saddle. On modern bikes the Specialized Roubaix or Sectuar achieve this very well.