I'll share my own experiences as I have also been in the same situation as you. I too have struggled with this dilemma of compromising on camera gear to save weight on backcountry trips. Every trip involves some degree of compromise on weight vs. gear. However, what I have come to realize is that when I've tried to save weight by leaving behind my "normal" camera, lenses, or tripods for lighter versions, I always regret it. Every time.
There is nothing worse than composing a shot and wishing I had those two extra mm's I would have had from my 14-24 that I don't have with my 16-35, even though it did save me precious ounces. Or, processing a shot and seeing too much noise in the recovered shadows because I was using my a6300 and not my D810. Or, having to accept more noise in a milky way/aurora shot because I saved weight and bought my f/4 instead of my f/2.8 and had to bump up the ISO. Or setting up a shot in a moving stream and getting constant tripod vibrations because I saved 16 ounces by using my dinky travel tripod. The list goes on. And it isn't just the practical reasons that I've just listed, it's also mental. When I'm composing a scene and am regretting not having my "real" camera, lens, or tripod, I start obsessing over it and it just takes me out of the moment and kills both my enjoyment of the experience and my creativity.
So, going forward I have decided that I won't compromise to save weight unless I am going to a location that I know I can easily return to (ie, the Sierra) or if it's a multi-week thru-hike, or if photography isn't a primary focus of the trip. The "once in a lifetime" trips I will bring my "normal" gear and save as much weight as I can elsewhere. If that means I do less miles in a day, or travel slower, or am just that much more tired at the end of the day, so be it.
Just as a point of reference, my last trip was a 7 day "once in a lifetime" type of backcountry trip with all off-trail travel over very difficult terrain that included lots of elevation gain/loss, unstable talus fields, areas of exposure, fording waist deep streams, and hellacious bushwhacking through very dense slide alder on steep and unpredictable terrain. So, weight was definitely a concern. I did a partial compromise and took my D810, 16-35 instead of my 14-24 and 24-120 instead of my combo of 24-70/70-200, and my travel tripod. In hindsight what I would have changed was to swap out the 16-35 for my 14-24 and take my RRS TVC-24 instead of my Gitzo travel tripod. It would have been a weight penalty of around 2 lb's or so, but I didn't find my pack weight to be an issue. My gear list for the trip is here
.
Even with this minimally compromised camera setup, my base weight without food was 35 lbs /18.5 Kg, and with food it was 50 lbs/22.6 Kg, which decreased by about 1.5 lb/day with food consumption. I think that is a pretty reasonable base weight and struck a good balance between quality camera gear and weight savings. I was with 5 other guys on the trip and 4 of them had full frame Nikons and the other had a Sony a7RII with a 11-24 and a couple of other lenses.
If one of your main goals on this upcoming trip is photography and if you don't think you will be able to do the trip again anytime soon, I would recommend you rent some lighter weight camera gear and do a "shakedown" trip where you can see just how comfortable you would be with some of the compromises you will be making for the lighter gear. It may be that you can live with those compromises, but it would be better to find out now rather than coming to regret it after doing a trip that you may not have the opportunity of every doing again.
