Cheers all for the input. Just a bit more background which I should have included earlier but was typing on phone. I have a 24-70 which is a lovely lens but I don't think it's at its best at the widest end of its zoom range and it's also very big and heavy for carrying around particular if I'm in the hills.
I'd fancied a 16-35 but a couple of things put me off, firstly they're not particularly small or light either and having finally been able to try one in person, I found it a little bit cheap feeling giving the hefty price tag. I'd still like one but can't justify the high asking price to myself.
In an ideal world I think I'd go for a 21mm Zeiss but they're very expensive and not very light either. That's sort of lead me to the Voigtlander which I like the look of on paper and reviews look fairly decent for my use but still not actually heard from anybody who's used one. KR raves about it but that usually makes me wary

The F3.5 max aperture doesn't put me off in the slightest as long as it performs where it counts in the F8-11 sort of range.
Oh and I really do value sharpness for wide angles but the other elements need to be right too. I don't want something that exhibits uncorrectable distortion either or something that flairs badly.