I've got several Ice breaker tops, the 150 weight is perfect for hot and humid conditions and going in and out of Air-conditioning and back into the elements (the highest temp I've worn Icebreaker in was around 42c and that was with a 150 long sleeve top as I was in the middle east). Also great for traveling these tops can be worn alone or under T-shirts and the retreat tops for extra warmth when it cools down or jerseys extra when the 200 weight is a little too much warmth. The icebreaker long sleeve gear is slightly longer in the arm length than I found my I/O Bio contact long sleeve crib top to be. I prefer the extra length, its not excessive but enough if your biking and layering with longer tops.
I don't even bother with cotton anymore, it weighs more in your pack and stinks if your sweeting, if you haven't tried Marino or thought it was just for winter warmth give it a go!