A standard zoom for D800?

I found that looking at previous work the vast majority of pictures I took were at focal lengths below 90mm.

I bought 24-70, it's very good, if size is an issue, and frequently it can be, then a slightly smaller zoom lens is not the answer. It's either a prime or a smaller camera system , personally I use a Leica with primes.

The real benefit of an interchangeable lens camera is that you change lenses, if you are looking for a one size fits all for a walk around then perhaps a different camera for those occasions, not the expected answer but logical .