Even with the ACBP projects, an 8800GTS should do more than 4k PPD.
It is definitely an odd situation, given that before loading up WinSMP, the clients did not have to fight for cycles. A couple things to check though:
- Under the Advanced tab in your client config, are both clients set to "Slightly higher" core priority? They should be.
- Try checking "Do NOT lock cores to specific CPU" and using a program like
PriFinitty 2 by Ed Wilk to make sure both GPU clients have access to both cores.