In reply to thomas the cat:
> Anyone know if it'll be too hot to climb in july, or too cold/snowy to climb in Oct.
Hi - I live just up the road from Arco. We climb down there ("down" because the lake is at just 70 m above sea level) from late September to about now (end of April) and it is wonderful - warm sunshine, olive groves, and almost no tourists. May is a bit sweaty.
In June, July and August it becomes a reserve for mad dogs and roasting Germans (and the odd Brit that took a wrong turn on the way to the Dolomites).
However, coming up towards where I live (altitude 500 m), and especially following the river Sarca up and westwards, there are some excellent cooler crags. You want to see the new lush guidebook in German and Italian editions.
Worth noting also that the same guidebook is causing an even more enthusiastic rush of Tutonic migration and the crags were already busy at Easter. (Fortunately there are plenty of undocumented crags ... I have a few mini crags of my own. Infinite scope for development.)
So I recommend October for Arco itself. July you would be better off higher up, perhaps falling back on Arco in the case of bad weather.