@ claptonman
The HD3850 is the fastest card supported by the AGP 8x bus. Any faster and you will see no improvement in performance.
@ OP
you dont necessarily need to upgrade to an i3. If you have a LGA775 Pentium4 or core2 series, then you could just upgrade the motherboard to one with a PCI express port (about 10 times the bandwith of AGP 8x.) and transfer all your other parts.