I have this derailer on my bike:
VeloBase.com - Component: Shimano RD-1050, 105
it works fairly well with the biopace rings that i got on the bike, but it seems that there is a fair bit of noise and it feels slightly clunky. I looked at it closely after lubricating the drivetrain and it seems like the two pulleys have some play/can move side to side. Is this a sign of wear or need of repair? The drivetrain feels good other than that.