Lens to pair with RP for travel

[Fast Glass]

I own also the 16-35mm f/4 IS and have used the 24-70mm f/2.8 II as well.

That is a really solid combo, not sure how heavy it would be together. But I'd almost be tempted to sell the RP, and take that money and the money you might invest in glass and get an R6. Or an R5 if that suites your fancy. I have used all of said bodies and it would make a dramatic difference. Probably more than the lens side of things since you got awesome glass right now that is not incredibly heavy. Of course this option wouldn't really save weight. But another thought process.

I understand you are trying to save weight, and that is legitimate. But if you have one lens and body in use. Then just have a very small camera bag just large enough to house a lens, if you even need it. You could be quite light weight in practice and in the field while using some top quality glass.

But the 14-35mm makes a lot of sense too and while a bit softer on the 35mm end wide open stopping down it is quite sharp. So it is a trade off, but not a bad one.

Not sure about your shooting habits. But something to consider is the weight and size/bulk of your camera bag or back pack. But this is definitely a place you might be able to recover some weight savings and if you want to save 6 oz's. This might be a place you can do it.

Hopefully this discussion has bounced some ideas and has been a wet stone for your mind.