Rating: 4 / 5
Cap 1 seems to have changed very little since it was called silkweight capilene back in the day. It dries very quickly, wicks pretty well (though not as well as cap 2), and most importantly feels light and airy in the heat. The lighter colors make a great sun shirt. It is also a very tough baselayer material, and will last years even under heavy use.
I consider cap 2 the more versitile fabric, but cap 1 is great in the summer.
(Believe it or not, the old silkweight stuff used to smell much worse after a day or two of use. The new cap 1 still gets fairly stinky.)