I would not worry about 35% cotton. My favoirte material is 60/40 nylon or rayon /cotton. The little bit if cotton adds breathability and I do not find it increases the dry time too much. I honestly do not like to hike in 100% nylon shirts - they just do not breath. The color of the shirt also adds sun protection - darker colors more protection. So if it is thin, go for darker colors.