Mark, I shoot an a900 primarily for water sports (water polo and swimming) and while it is ok for swimming, it is tough to use for water polo. I have to wring every bit if skill and patience from my body just to take decent shots. If Sony can come up with a decent AF tracking (the a900's is useless for water polo, as I am sure most AF systems are when trying to focus on a water polo ball being tossed rapidly from player to player) I will stay with them. I may even jump to the a77II for the extra reach.
The a900 files are terrific, but you know, to everything there is a season. Give the mirrorless cameras a try. Many people love them, and the files seem nice.