Well, I've tried a few different road bikes from a few different shops so far and in a few different sizes. Cant really say anything jumped out at me as being "the one". TOday, for kicks, I tried out a Cervelo p1, 58cm triathlon bike. Since it was pissing rain outside it was only on the trainer and I will take it out on the road first before I pass judgment but, speaking as a person with back issues, it is infinitely more comfortable on my back than any of the road bikes. I can completely relax all the muscles in my back and just rest on the bones in my arms,, which is how I do it when I try to lean over to work on a car. Granted all the other bikes were on the road, not trainers so maybe things will change when I actually have to pedal over stuff and I was only on the trainer for a few minutes at a time then paused to make adjustments.
I was really hoping for the opposite to tell you the truth, now I am very conflicted to the point of forgetting it and sticking with my mtb + slicks for a few more months until something golden falls in my lap.
Eric