Thanks. My impression is that nothing through the 500 series provides a substantial improvement over the 295 - the numbers seem to indicate the improvements would be moderate. Am I misreading things? Would the cost of a 500/600 series be worth the improvements over a 470/480?
I do have the list of accelerated operations and I use a good many of them.
Your CPU is likely the biggest bottleneck in your current rig. You can confirm this by monitoring your CPU usage (Task Manager / performance tab) and GPU usage (I use MSI Afterburner which may also work to monitor GPU on non-MSI graphics cards).
My vote would be save your cash and put it towards a new motherboard, cpu, and RAM when you have enough. Good Intel i7 options would range from around $600 to $1000 and would completely blow away your Athlon so far as performance for Premiere Pro CS5/5.5/6 goes.