when I went to tour in the Pyrenees, I previously had a 50-40-28, 12or13-30 rear. Changed the 28 to a 24 (shifters on downtubes, frictionless front derailleur shifter) and the 24/30 combo ended up being fine for the weight I was carrying.
I cant comment on the limits on the front chainrings limits due to the derailleur (as I dont know this stuff) but what I would recommend or comment on is that when loaded, I very very rarely used the 50 tooth chainring except for finding inbetween gears more in the middle range.
Yes, there were downhill sections, but in the big scheme of things having higher gearing wasnt really a need for me. What was more useful was having more options of gear inches to find an "inbetween" gear with a headwind, or whatever.
as for the low gears, your present low 26/32 is about a 21 gear inch, which is pretty much the 24/30 on my old touring bike. You have already stated that you want lower gearing, and I realize that the weight of stuff on your bike is the real kicker here. I am slight (140 max) and I learned touring to be very minimalist, despite having a tent (heavy-7 lbs), campstove etc etc etc and for me the change from the 28 granny (was about a 24 or 25 gear inch combo) to the 24/30 combo was great. Didnt have to use the "new" gear often,but it was nice when it was needed--and essentially it was "one lower gear" than I had before.
a 24/34 is 18 gear inches, pretty darn low. I wish I had weighed the stuff I used to carry on my bike (2 rear bags, 2 small front ones, handlebar bad and tent) but I honestly dont know how much it was--perhaps 40lbs min I would say. I guess what I mean by this is to really look at what you can reduce in your packing. I learned my having too much what to reduce, and less weight would mean less low gearing to have to set up.
hope my touring experience vis a vis gearing is of help. I am not a strong rider, probably fairly average, so I think my gearing recommendations are alright. (I used the 24/30 in the Pyrenees, American west coast--I would say that San Fransisco steep hills were where I was very grateful for the low low)