stew2, your link takes me to the main page of the forum
Not knowing ATI I couldn't tell you much but, the little I know, there are times when you tend to bottleneck your GPU with other resources when you upgrade.
Example: Your PSU is just right for the GPU, then you upgrade the GPU and now, the PSU is no longer able to move the GPU 100% so it lags a bit, hence, your drop on FPSs.
Again, I am not saying this is your problem