We did it nearly 3 years ago...Buenos Aries - Valaparaiso. Though it was the start of March (end of their summer), it was hot in BA, but by the time we got to Cape Horn it was down to about 9C. It was a beautiful sunny day and almost a flat calm. The captain even stopped the ship so the front half was in the Pacific and the back half in the Atlantic! Any questions, ask away.