As a general rule, two processors which have similar die-sizes and are produced using the same manufacturing process have similar performance ...
Now, this doesn't tell the whole story because a processor that is designed for a specific task is likely going to trade-off general processing performance in order to increase processing performance for their specific task; for example, a very modest GPU can easily outperform your CPU in rendering tasks but wouldn't run a word processor well (if you could even program the Word Processor to run on the GPU).
The XBox and PS3 CPUs are two processors which have similar die-sizes and are produced using the same manufacturing process, the main difference between them is they have drastically different architectures which should give strengths to each processor under certain tasks.
