Backs are funny things. Sometimes stretching out over an upright bike can be better for a bad back, sometimes it's excruciating. For bents, suspension is mostly for control, especially if you have a mesh seat back to absorb shock. Something like the Expedition with slightly fatter tires might work fine without the extra weight of suspension.
Group rides will be a challenge on any trike. Or maybe I should say they'll require a change in mindset. Trikes don't mix with uprights. They can't draft off you, and you will have a different speed profile -- mostly slower for a trike. If speed is going to be semi-important, look at the gearing numbers for the various trikes. The stock gearing will tell you a lot about the speed capability the trike has. An 85" top gear is telling you that the manufacturer didn't design it to go fast. Carbon shell seats provide good power transfer, and if they fit they're supremely comfortable; but if they don't, there's no adjusting around them.