It would seem to me that in a case where the rider has worked to get gear weight down to 20 pounds or so, adding a 13 pound trailer would be a strange thing to do.

It is certainly easy enough to give the roubaix a try with the loaded saddle bag and handlebar bag and see how it rides before changing anything else.

BTW I have been considering something somewhat similar to what the OP is suggesting. I am considering using two smallish front panniers instead of a saddle bag with the tent hung from the saddle. Since I have gear and pannier weight approaching 20 pounds a 29 pound bike seems less and less desirable. I would not be putting on a Brooks though. I find my road bikes supremely comfortable and strive to use the same riding posture on my touring bikes, so no adjustments are required for comfort.

I would be curious to hear what gearing options the OP is considering.