PlayStaion 3 had a RSX GPU which was comparable to GeForce 8800GT in performance. RSX called Reality Synthesizer is a propretary graphics processing unit developer by NVIDIA and Sony for PlayStation 3. First RSX GPUs were made in 90nm process but they were shrunked in 2008 to 65nm and to 40nm in 2010. It was a simple gpu based on NV47 chip, which was previously designed for GeForce 7800 cards. RSX has a core clock set to 550 MHz and a 256 MB GDDR3 memory running at 700 MHz.
On the other hand we have XBOX 360, which is already powered by ATI Xenos, a custom gpu designed by ATI, which was based on R520 core (similar to Radeon X1800/X1850). Graphics were computed by two chips, GPU and eDRAM which was a 10MiB memory clocked at 500 MHz with unbelievable bandwidth of 256 GB/s.
Forbes quotes former AMD staff who mentioned that Sony may begin using a new GPU, therefore based on manufacturing from another company. This information is somewhat confirmed by AMD, which is expecting an increased revenue from non-computer graphics.