It's still too early to tell. This would not be the first time that speed improves after a maintenance and then it slowly gets worse every week until it looks almost like before the maintenance.
Is it possible that the degradation in performance is due to more developers building more apps and driving more traffic to App Engine as time goes on?
The performance degrades too quickly for this. In two or three months we might be on our old performance level, again. Well, I seriously hope that we'll stay fast this time. Only time will tell.