/ Clothing for big wall in Peru
Don't know anything about what weather you would get there, and from your profile I would imagine that you've probably got plenty of experience to make an educated guess from - but if I have a decent softshell with me, I'd always go for the lightest waterproof I can find as I'd only put it on for hard rain/wet snow. I reckon a windproof (pertex etc.) can give you as much protection as most softshells, so for pure lightness that might be the way to go - but if you are doing lots of rock climbing (as opposed to say hiking or mountaineering on snow) that's one place where the tougher material of most softshells might be an advantage over a pertex top.
I've found I can get a bit sweaty inside primaloft insulated midlayers (http://www.ukclimbing.com/gear/review.php?id=4447) but again probably wouldn't be a problem when rock climbing as its less aerobic than XC or snowshoeing etc.
Don't know about September - we did it in July and I'm guessing (and it is a wild guess as we didn't have a thermometer) the coldest it got on the wall at night was probably about -10C.
During the day the original route is in the sun till afternoon so climbing in base layer was OK, once in the shade we climbed mostly in soft-shells. I also had a light-weight primaloft jacket for belays, and also a more heavy-duty primaloft belay-jacket for night-time as well (I get cold easily).
To be honest I think it depends entirely on what style you want to do it - if you are going to do it in one day then you can get away with not carrying too much in warm clothing - but it did to snow quite heavily after we finished so also depends how much risk you want to take with gear.
Hope that helps.
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