Board Thread:General Discussion/@comment-3123266-20140303175822/@comment-3123266-20140805204243

From what the collector said, there does not seem to be any real differences in capability among stones.

Thanos is a master manipulator. He has the infinity stones EXACTLY where he wants them:
 * Scepter - Earth
 * Tesseract - Asgard
 * Aether - Knowhere
 * Orb - Xandar

That leaves the fifth stone for an upcoming movie. Maybe it is the Eye of Agamotto?

Thanos would have the sixth stone. From Infinity Gauntlet #6 "From the one, I reach out to the five!"