Sean i somewhat agree with Rooz.
i played around with the Tammy 70-200mm and the Sigma 70-200 HSM and the Tammy was pretty slow compared to the Sigma. pretty sure the Sony SSM will be much faster.
as for the body choice, i really can't comment since i'm not in your situation and not much of a sports fan. the a700 has awesome AF speeds so it has that going for it.