Okay so the first time around the performance under relatively light load was pretty stable. Now given that we are at the Quota Denial Coral would this impact the performance?
First off look at the scale, its not as bad as it looks. We are still talking normally about a 10% range from Min to Max and even the worst case is 16% which is hardly a major issue. But is this a surprise?
No it isn't. The reason is that because of the quota that we are breaking (page views) we aren't actually stressing the CPU quota as much (although using several milli-seconds a second indicates that we are hitting it quite hard). That said however it is still pretty impressive that in a period of time where we are servicing around 90 requests a second the load behaviour is exactly the same, or arguably more stable as the min/max gap is more centred around the average, than when it is significantly lower.
So again the stability of performance of App Engine is looking pretty good independent of the overall load on the engine.