I think it's important to remember that Sony has unveiled far more information about their hardware architecture than Microsoft has. Saying that PS3 will be faster is premature.
In fact more SPEs, threads per CPU, or CPUs does not indicate that the games will be any better; all it means is developers will have more processing power available to them. To take advantage of this new power developers will have to write their software with multiple software threads. Currently, most games are written to run in a single thread. Games that have been written in two threads for multiple CPU computers have shown a negligible performance gain.
The real problem is not general purpose CPU power. That's why the original Xbox could get away with a 700MHz Celeron. The bottleneck in today's games are the GPUs. The console with the better designed GPU will have the best games.
XBox 360 and Poor Image Quality-
At the E3 trade show Xbox games are not running on console hardware they are being run on Apple Powermac G5s. Image quality will be better when the Xbox is delivered.
Link