A book I have mentioned previosly, The Shape of Ancient Thought, by Thomas McEvilly, also provides highly detailed comparisions of ancient Greek and Indian philoosphies, particularly in relation to Platonism, Neo-platonism, skepticism, Buddhism and Vedanta. It argues pretty convincingly for a great deal more commonality between the two traditions, at least in ancient times, than is previously been acknowledged which he says traded many ideas and contacts along the ancient silk routes. He says it is possible there were Jain and Buddhist missionaries in ancient Alexandria, and that the Upanisads were known to the Church Fathers.