One thing I didn't say in my previous post...
I found that I really didn't mind losing the higher end of the gear ratio range with my unconventional setup for the ST, so getting a super wide ratio setup isn't as necessary as people think IME. You could just go however low you need at the expense of the higher end of the range if necessary. That makes for a lot more flexibility in what you can make work. With my light load that wasn't very low and I was able to use the original short cage derailleur. In my case the range was 25.1 to 87.8 gear inches and I never found either end to be inadequate for the load I was carrying. With the limited high gear I just spun up to speed with a briefly really high cadence at the top of a descent and then tucked and coasted.
I was riding with a strong young guy (I am an old retired guy) and I didn't have trouble keeping up anywhere that higher gears would have helped. He climbed much better than me on long climbs, but I had no trouble staying with him on the flat sections. Strangely enough I was often faster than him on certain types of rolling terrain. I was carrying a lot less and rolling terrain is usually my forte, I love to hammer on rollers, so I guess it makes some sense.